Yeah... the 56k is referring to kilobits.
More precisely it is referring to the maximum speed the modem can achieve, which is: 56 kilobits per second.
There are 8 bits in a byte. Therefore it is a simple operation to do 56/8 = 7kilobytes per second on your absolute best day. However, the thing they neglect to tell you: that is total possible throughput. It encompasses both downloading ("recieving") and uploading ("sending") data. So you will really only get a 3.5-4 kilobit per second transfer rate in either direction.
I hope you followed that. I tried not to make it too confusing... think of it like a speed limit. Cable modems and DSL are like the freeway, and 56k is like driving past a schoolyard full of kids. In one case you have the possibility of zipping around cyberspace... in the other you're relegated to crawling across your cyber-lawn to fetch email.
P.S. AMD Athlon XP 2200+'s run at 1.8GHz, but perform at least as well as Pentium 4 2.2GHz processors because they are far more efficient
Good choice! Motherboard could have been a bit better though... next time I reccommend an Asus A7N8X or A7N8X-E (the E stands for deluxE apparently...)