1GB is fine for BF2. With your graphics card and RAM you'll be able to run it with all settings on medium which is fine, the most important things in BF2 to have turned up are shadows and view distance, because the retards who have those turned off are at a disadvantage.
And all those modes that Wheelman posted for CS:S are server-side mods, which add new types of gameplay. Regular CS:S has de_ maps, which involve terrorists with a bomb trying to blow something up, and cs_ maps, where terrorists have taken hostages and the counter-terrorists must rescue them.
de_dust2 and cs_office are the best official maps!