I do lots of VO, but use a bit more expensive software and hardware (Pro Tools & AKG & Sennheiser condenser mics).
However, even with a cheep mic you can get good results if you isolate the voice. IOW, if you record in the same room as the computer, there will be fan noise. Actually, unless you isolate, there will be LOTS of noise. The human ear learns to filter out all the non-stop extraneous sounds around us that play out all day. But the mic picks up all of it. Also, acoustics play a huge part in the quality, and most hard, bouncy computer rooms sound like garbage.
On a shoestring, this is what I would do:
Buy or borrow a good mic (Ebay, used, condenser, or even an SM58 is better than nothing).
Buy an interface so you can bring XLR into your computer (or even work it down from 1/4" to the 1/8th" inch most sound cards use, via Radio Shack [Augh!! I can't believe I said, Radio Shack!!])
Run your wire into a closet filled with clothes. You would be amazed how much better the VO sounds recorded in a close closet, and many excellent pro audio people have used this trick when they first started out (meaning, they were too broke to build a recording room). But get out of that square, hard, noisey room. Even tossing a big wool coat or blanket over your head is better than nothing.
Unplug refrigerators, air conditioners or any appliances that have motors running. Those motor sounds transfer through walls up through mic stands and wreck havoc with the recording.
Shoot the neighbor's dog.
Record with any software that uses at least 16 bit, 44100Hz (Sonar is a good one mid price, but there are lots of them for even less).
Keep the mouth of the VO person
close to the mic. You can't get too close as long as you don't overdrive the mic (or clip in the software).
With digital, let the level bounce to zero at the highest levels.
Use a compressor plug-in. This can make the difference between armature and pro sounding audio when used properly. On VO's, I'm not afraid to really squish it.
Get Home Recording Magazine and read it. There are lot good tips for the DIY VO person.
That's my free advice, and it's worth what you paid.
Have fun!