Welcome! to Team Anandtech! 😀
I don't think adding more ram will specifically help SETI, but may help the overall performance of the PC, depending on the applications you run, how many are open at the same time, etc. 🙂
There is a Linux version, but it is slower than the Windows version. Depending on the setup, some have gotten best results by running the Windows version in WINE in Linux. 🙂
MrFluffy (my son) and I have a dual PPro180@200 running Win2KPro and functions as our home SETIQ server and also crunches away at SETI. 🙂