like the others have stated - stick with WPA, but i get the impression from your post that this is bugging you somewhat!
the fact that you can see your network, and that it allows you to connect via WPA, suggests that this is a simple problem (i'm guessing there), and the way you described your connection forever cycling and prompting for a key, suggests this may be a passkey/passphrase issue.
i'm not suggesting that this applies to you, but from my experience having read numerous wifi connection issues on other forums, where the same issue is described (ie a connection cycles and keeps prompting for a passkey), it usually has a very simple explanation - although this usually applies to 128 bit WEP rather than 64 bit. For the benefit of others that may be having this issue with 128 bit WEP then it could be that you're simply selecting the incorrect wireless security option.
Many wireless routers - particularly those supplied by ISPs, come pre-configured with 128 WEP security (not always, but quite often). Turn the router over and it'll tell you that you have 128 bit WEP security, and they'll be a 13 - character passkey. This however is NOT a 128 WEP passphrase, rather it is a 128 bit WEP ASCII key - and many make the mistake of selecting the former rather than the latter when trying to connect (i come across a few people who have had this problem and have assumed it is a driver issue).
I'm not suggesting something as simple as this applies to you, but this may help others who are having connection issues.
I too use a Belkin wireless USB adaptor, and despite all the problems others appear to have, mine worked perfectly in linux mint straight out of the box! didn't need the windows drivers; the pre-installed driver on LM for my chipset (zd1211rw) worked a treat!
i'm new to linux mint, and fairly new to linux, and i have to say it is the best distro i've come across. everything justs works!