I decided to try building my 1st system.  

  Here's what I have:
CM Storm Scout case
Intel Core Duo E8400
Gigabyte EP45-UD3P motherboard
Mushkin PC2-8500 2x2gb memory
Corsair 750W power supply
Western Digital 320gb HD
EVGA 9800GTX+ 
1. I mistakenly bought Windows7 "for system builders", thinking: 
I'm building a system - that's for me  
 Can I use that or do I need to send it back for the retail version?
2. I am not planning on overclocking anytime soon. 
 Is the stock fan/heatsink that comes with the cpu OK?  Should I use Arctic Silver instead of the stock paste?
3. Will the 4gb of memory suffice or should I get more?  They should be the same specs and timing, I assume.
I have a Bluegears sound card from my current system that will be swapped over.