RS loading screen freezes in Ubuntu Help please?

I switched over to Ubuntu and started using their xubuntu desktop to reduce some ram. I'm running a Pentium II at 300 mhz, 256 mb of RAM. I sent a query to Jagex, but they said something about going to windowsupdate.com

So heres the problem:

I load runescape. It loads fine for the first few seconds and then freezes at the Getting Updates screen. I'm assuming the problem is that its trying to write a file onto the harddrive but security settings prevent it. (I remember loading it in windows and I needed a to create a rscache folder.) I'm thinking I have to create the same folder but I don't know where or I can lower the security settings; but how to do that? Any ideas :|?

Thanks in Advance