Swapping CPUs is slightly more involved then RAM. Mainly cleaning the Thermal Interface Material (TIM), aka CPU paste, off of the CPU and heatsink. That is easily done with Isopropyl alcohol and a clean lint free (Micro Fiber) cloth.
For applying new paste there are several schools of thought on this and is a huge ongoing debate on many techie forums but I won't bore you with it. Instead I'll point you to rational sources for some quick tutorials.
NCIX: Installing Thermal Compound (NCIX Tech Tips #11) Video
[H]ard|OCP: Thermal Paste Shootout - Q209 (pg. 3 - Applying the paste)
Note that the NCIX video demos two CPU coolers that are not used much anymore. If after looking at your system, you find it hard to figure out then take a pic and post it. Then I can find a youtube video (hopefully) that matches your cooler.
The 9800GT is an old GPU. A dinosaur in tech terms. I offered as an alternative to shelling out cash. But to answer your question, there of those 430s with totally smoke the 9800.
F$
PS. No reply yet to my first PM about helping you but I did find Three Pentium 4 CPUs in my collection. Two are Socket 478 so they will work with your current MB and the other is Socket 775. I also found a Socket 775 MB that has (x2) PCI slots and (x1) PCIe x16 slot. I was also able to dig up the 420 Watt PSU I mentioned before.
I forget to go through my RAM collection but I promise to do that tomorrow.