Few Questions About Mobile Broadband Dongle For PC

Just a few questions about USB Mobile Broadband.

Im currently using a wireless router which is located downstairs but my uncle is doing away with it as it slows down the net connection to the 2 computers downstairs.

Only thing i can do is get a USB dongle but not sure where to start.
I would only use it for sites like bebo, tagged & facebook & msn.

Would it be worth getting or would it be REALLY slow ?
Also would i still be able to view my contacts webcams on msn ?

What would be a good network to go for & what kind of speed would i be looking for ?

It would probably need to be a prepaid dongle as i have a poor credit rating lol

I seen quite a few on ebay & some computer sites, but dont know what im looking for.

Cheers for any help i recieve.

:/