I definitely wouldn't get another USB modem as you are likely to see the same problems...if indeed that is what is causing your drop-outs. The 330 isn't the best hardware for up to 8 Meg but problems tend to be limited download speed, not dropped connections. Have you optimized your phone wiring as per the guide click here
I would still advise you upgrade to a router anyway. All you would need apart from the modem/router would be to fit a network or ethernet card in your PC if it doesn't already have one unless you want to go wireless, then you would need a wireless PCI card or a USB dongle.
A lot of people recommend the Netgear DG834G wireless modem/router (you may not need wireless but it's only a few pounds more than the wired version) as it's very easy to set up. Having had one and since replaced it I would recommend the Speedtouch 585v6 for wireless or the 546 for wired.