Motherboards, graphics cards and RAM

you probably will need to buy a new cpu, you gotta check what socket your current CPU is and it probably is 775 (same like mine) and currently on the market there are like no good motherboards for 775 that is worth getting.

You probably will need to upgrade all of it.

upgrading your ram couldn't hurt if you use windows 7. 6-8 GB should be sufficient for anything.

You'll probably need to upgrade your power supply as well.. It'd just be better off just building it from scratch and see if you can reuse the harddrive, disc, case.

I'd stick with the motherboard you have, as getting a newer AMD motherboard that's Socket AM3 isn't going to serve much purpose if you're not upgrading your CPU. I'd just buy more RAM and a new video card.

You say your motherboard is DDR2, so the cheapest CAS5 800MHz 8GB kit out there is this:

http://www.newegg.com/Product/Product.aspx?Item=N82E16820220409

Then I'd go with an EVGA card.

http://www.newegg.com/Product/Product.aspx?Item=N82E16814130604

EVGA has the best warranty in the business. And that's probably the best card in your budget, and to be honest, your CPU is bottlenecking the performance of the graphics card, so there's no need to get anything higher than it.

A combination of the two should be sufficient if you're not upgrading that CPU of yours. :)

EDIT: Seeing UltraJesus' post, I forgot about your PSU. Post on here what brand, wattage, and +12v amperage your PSU has (or a model number would be better), that way we can evaluate if your PSU can accommodate a new GPU.

I dont see the reason why people recommend someone have 8gb of ram that 1.) Hasnt stated they do any kind of graphic design or 3d modelling and 2.) Stated a rather limited budget.

Taking New Vegas with the NVSE+4gb aware + graphical mods, I dont see above 3gb of ram usage. (Running 64bit OS BTW) with a slew of apps running in the background.
1.) Unless you actually have a 64bit OS there is no point in going higher then your current 3gb. Your OS wasnt stated.
2.) Assuming you HAVE a 64bit OS, 4GB is plenty if your not doing 3d or graphical modeling.
3.) PSU is a consideration for any graphics card upgrade, as is your current motherboard. If you have enough wattage to support dual or very high end graphics cards is important. As is if your motherboard can run multiple graphics cards.

With the limited information posted I assume..
1.) Your motherboard has 4 slots for ram
2.) Your motherboard has 1 or MAYBE 2 PCI-E slots.
3.) Your PSU is rated for 500< >800watts

A GTX460 would be around the area to start looking. If your PSU is more robust then by all means a 6990 or GTX590 could be your card.

Ok, I am going to write this in Portuguese, nothing wrong on that :P

Ano passado eu trouxe 2 HDs e memória para o Brasil. Não tive incomodações fora o peso de carregar tudo isso nas costas.
Sobre as tuas compras, eu te aconselharia um processador novo que consiga usar teus outros componentes. Não deve sair muito caro.
Eu trouxe 4 (2+2) GB de memória DDR3 1333 MHz da Corsair. Nunca deixei que rodar nada no computador por problemas de memória. Além disso, sai barato.
Se fores realmente pegar uma nova GPU, provavelmente vais ter que comprar uma nova fonte. Eu comprei a minha no Brasil, achei que não valia o transtorno. Além disso, a minha placa-mãe nova precisava de uma fonte melhor devido a pinagem de energia dela. Te aconselho checar isso.

Qualquer coisa, entre em contato comigo.

Eu acho que vais te incomodar um pouco com o espaço que uma placa-mãe vai ocupar na bagagem de mão.

Ok, guys, please tell me: should I change my motherboard or just buy compatible DDR2 RAM and graphics card?
Thanks to all who commented and helped me until now!

definetly something with new socket r (lga 2011) look through on google

Keep in mind if you PC Case supports either ATX or only Micro-ATX Motherboards/Mainboards.

I'd say any AMD 970 series motherboard ($~85), 8gb ddr3 1333/1600 ($30 - $50) and 6850/6870/560TI ($140, $160, $250) depending on what your power-supply can handle. If you need a new power supply get at least 650w (Antec/Seasonic/XFX/Corsair ect), no cheap unknown brands. ($90)

So around $255-$385 without new psu and $345-$475 including new psu.

What's your current case, motherboard, and power supply? (Edit: Also, what's your current operating system? 32bit or 64bit?)

I would like to know what your case is in case it only supports micro-ATX/etc type motherboards. I doubt that's the case though, but I would rather make sure first. Your case could also be a problem in regards to video card length. I would like to know your power supply to determine how well it could handle an upgrade to more powerful parts. You never stated, so as far as I know you have some pre-built Dell that's not capable of handling a large upgrade.

Depending on your motherboard a processor and video card upgrade would be far better than an upgrade to your motherboard, RAM, and video card. How come you do not want to upgrade your processor?

Best bet is video card Check here for the best buy in your price range and 4gb of ram (i would say 4gb preferably just buy 2x1gb sticks if you have two open slots in your mobo). If your psu is not 500w and a descent build I would look into upgrading that as well.

Do not upgrade your motherboard unless you have a psu. Like TheB$1 asked. What is the model numbers of your current setup. whats your psu. Everyone is assuming that you have a descent enough psu and mobo to upgrade just your ram and video card. I agree with them ram and video sounds like the best way to go but unless your psu will support a card you will need a psu. they are also assuming you only have 32 bit or 64 bit windows. etc. does your mobo have any open dram slots?

(the 6770 is a great card for the price imo)