Haha... well at least you bought something usefull!
I presume that since your looking for an amplifier you bought "passive" (unpowered speakers)? Are there other specs for the speakers?
RMS is generally not a very usefull rating to use when picking out an amp or really for much else other then as a sales angle.
here's a link I found on the internet that talks about it a bit.
http://www.hifi-writer.com/he/misc/rmspower.htm
Depending on what your looking to spend on the amp and how nice your speakers are, you can find them from dirt cheap (with the quality to match) all the way up to crazy pricey. Whatever you get though should work with the mixer you end up getting for your computer (as the mixer should have a Digitial to Analog converter built in) and should have outputs for standard jacks (XLR or TRS). I picked up a book from amazon called "the sound reinforcement handguide" that i found exteremely helpfull in putting together a little home stuio. A friend of mine that does pro sound for a living suggested picking it up to get some good general sound knowledge under my belt.