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USB & Internal Dialup Modems use processing power from your main CPU, External DO NOT!
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If you have the money to purchase and external one, make sure it is either Creative or 3Com they are the best on the market, most stable which is best for online gaming.
However there are alot of cheap Broadband deals now, with Cable/DSL/ADSL - ISDN - T1 etc...
if i were you check about the prices as within the US and UK it is just as cheap as an all inclusive Dialup ISP now!
$24/month for AT&T 256kb stateside or £15/month NTL:Home 128kb line - both with the stability that only broadband full digital connections provide!
Anata aru kowagaru no watashi! 