Also. As far as the build is concerned.
Are there any items from your old machine you are planning on using?
Hard drive,
CD optical drive,
Sound card.
Case, Etc?
Obviously the more of those you are using. the more money you have to blow on other components
So a list of those would be helpful.
And dont forget to include the operating system in that equation.
For XP SP2 its gonna run you about $135.
So if $800 is a hard limit
That brings your total funding for parts down to $665