D630 is a little old to be running Windows 7, but it can do it. I believe the system maximum is 2x2GB SODIMM DDR2, it will be rather expensive to upgrade (though you didn't actually list how much ram you have now)
You can't just install fans, a laptop cooler might be something to try, but given the age of the computer it probably needs to be taken apart and cleaned on the inside and the fan replaced. I don't believe Dell will have parts, but possibly. If not you should be able to locate parts on Ebay. (That is what we did in the last year of use of Dell 620 and 630 at our company, hinges and bezels were often broken after a few years use)