It's on the Wii. I wouldn't bother getting one unless you're hell bent on playing The Umbrella Chronicles, either.
Wesker survived by injeting a virus into himself, which William Birkin created, shortly before Chris and Jill entered the laboratory room that the Tyrant was in. The virus brought him back to life, along with giving him superhuman powers. He then just about managed to get out of the mansion in time for the explosion. This explains why he reappeared in Code: Veronica, and in Assignment: Ada (and the awful Seperate Ways) in Resident Evil 4.
It has also been confirmed that he actually does return in Resident Evil 5, along with an older Sherry Birkin (all according to Wikipedia).
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