This is pure speculation but:
Have you tried headphones to rule out the possibility of speaker interference? How about different speakers?
Since the dell almost certainly has intergated audio, perhpas you should consider spending $20-$30US on a cheap sound card. If you are too cheap to do tat (which is understandable), perhaps try moving the modem to another PCI slot. I don't know why that would fix the problem, but you never know with dells and integrated crap...
Oh and for college, unless the T1 is yours or shared by only a few people (it is porbably shared with the entire dorm building, perhaps more), then it may very seem slower than dial-up. Our school has a T1 I think, and either their router is crap, or traffic is really high, but it runs at about half the speed of dial up for websurfing (runs at 400ish kbps for downloading though)