Wow! V.90 modems already! Wow wow! They're only $100 in the States! Too good to be true? Er, yes. These are the sadly misnamed software modems that use your Pentium to do the sums that decodes the noises that come down the line - this saves a twenty quid chip, but you still need the interface card to plug things into the phone line. There's nothing wrong in theory with this, except that while your Pentium is working hard it's not available for other jobs - in effect, your 233 MHz Pentium is running like a 133MHz machine.
Do the sums: you've saved twenty quid and wasted the couple of hundred quid you spent on buying a faster machine. Or you could buy a slightly more expensive modem and have done