It happens to me too, i fixed it A BIT killing the explorer.exe process, i dont know why, i just tried it and it worked fine for about 6 hours without problem (yes, i let my laptop/toaster open all night lol)
if it doest work you can still try to update the client
-im using a 2gb ram Netbook with 1.6HZ intel quad core, and a 200-480kbp/s internet connection.