pbfrias17 :
I ordered all my components on different days. My ram is the last thing to come and it won't come for a couple more days. Is it ok if I pop in 2 modules from an older (around 2007) desktop? This is assuming my new mobo is compatible with the old ram.
Yes, it is natural to test the new build with known working memory regardless of the age of the memory. But considering the year you are mentioning I think the old memory is DDR2 and the new memory will be DDR3 for sure. So they are not compatible with each other physically, electrically etc.
But if you have compatible DDR3 memory with you then you can try it in the new build and it will work fine. Cheers!!