Well, the Athlon XP is a really outdated CPU. I recommend something like this:
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115004
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131153
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150229
2GB of RAM is fine for vista, that's what I have, and it's very smooth. With the parts above, you should be able to run it with AERO with no problem.
If you do stay with the Athlon XP, I would really recommend upgrading the graphics though, to this:L http://www.newegg.com/Product/Product.aspx?Item=N82E16814241040
But I think you should really just get the parts that I said, or keep what you have and stick to XP.