You can, but you really shouldn't. ;) Do yourself a favor and play ME1 first.
What happened in ME1 is explained in the beginning of ME2 (if I remember correctly), so you won't have any problems following the plot.
That being said, you will miss out on so much excellent story. There are places and NPCs that reappear, but you won't recognize them. And since you can import your savegame from ME1 decisions you made in the first one regarding the plot and the relationship with your teammates will influence how ME2 plays out for you. The interaction with other characters is one of the best parts of these games imo.

In short: Playing ME1 (and the complete series for that matter) is highly recommended.