Topic: Recording voice over

Yes, a big difference. Condenser mic and a preamp is the way to go. Note that there are both "small diaphragm" and "large diaphragm" condenser mics, you'll be wanting to use a large diaphragm one. A mic to suit your needs may not be as expensive as you think, check out models made by Rode. If you're recording in to a computer your AD/DA converter will probably have a preamp built in. Just as important as a microphone is the room that you'll be recording the voice over in. It should be pretty dead and very even sounding. It's very distracting to hear a room sound or excessive boominess on narration. Given these factors you might get the best sound by hiring out the job.

Blankets or curtains can absorb mid to high range frequencies but are not thick enough to absorb low-end frequencies. Only mass can do that, like six inch thick fiberglass. The recording PC has no affect on the boominess. The fan noise itself could be picked up by the microphone, depending on placement.