I think some of the people here might have misunderstood you. Either that or I'm misunderstanding. I'm assuming you mean both CompUSA and BestBuy are selling something for $100. CompUSA has the 10% off coupon that works instore, so if you were to use that the product woudl be $90 at CompUSA, and you want to know if BB will match that.
I tried this exact thing on my Radeon9800 pro yesterday. I ordered it from their warehouse a couple days ago, and printed out the 10% off coupon to BB yesterday. The guy says no at first, saying you need an actual coupon. I tell him, well on the coupon, it says you need to PRINT this coupon out to use it in store, so obviously it's an internet coupon that works in store. He asks one of the "supervisors" who says no. I say ok, can you go check if my 9800 pro has arrived yet. He dissapears for a second, comes back and says it's not here but manager says I can pricematch it.
Cashier somehow ends up with 266.99 (299.99 - 10% isn't 266.99 iirc), but I was successfully able to PM the 10% off coupon, but it was a YMMV.