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)
Your Dell needs to be open to clean heat sink, fan and put new thermal paste between eat sink and processor/graphic chip. After this it will run colder. You can buy a cooling base to put the laptop on, but untill you have the cleaning made it will run hotter with time.
You can easilly upgrade memory up to 4GB using 2X2Gb DDR2 667MHz (PC2-5300) SODimm Ram sticks and any normal 2.5" Sata Hard Disk.
That computer hardware supports Windows 7 32 or 64 bits. AT LEAST 1Gb ram for 32bits and 2Gb ram for 64bits for it to run ok... If you upgrade to 4Gb it will run very good. Some device drivers may give you a little work to get, but Vista drivers usually are accepted