I've just been tidying my office and I found a pile of old checks worth about $5,000!

At first I thought it was my lucky day but these checks are all at least two years old. Now I'm wondering if I'll get anything for them.

Do you guys know what the rules are concerning old checks drawn on US banks? Most of them say 'void after 90 days' on them - but checks say that in Britain too, and ours still get accepted even if they're ancient. What's the score with US banks?