Yes it is. Just stick both in and see if it works.. You might as well. But the 1066 ram will run at 800 speed because it will be forced to run at the slower speed. Then go and get a 64bit OS.
FYI, 32 bit OSes recognize a maximum of 4 gigs. This includes video card ram, your Bios, and all that other stuff. Somehow everything else comes first, then the system sees whats left for the main system ram (actually if you think about it it makes sense). That means you will see less than 3gigs of your total ram