Sounds like a client side issue, and my first thought when seeing your specs is that 512MB is low even for Windows XP, never mind running anything else, but that's what I started out with very well myself. Look into raising your RAM by a 1GB and I'm sure you'll notice a difference, but I don't honestly expect that is the real issue.
Just a suggestion : try making a fresh administrator account in Windows, login to it and run Ryzom there. (MacOSX troubleshooting trick - bypasses user account preferences.)
Then try asking for help on
Klients.