Audacity will probably be your best bet for what you described. Record in 24-Bit 44.1 for CDs. Until you deal with high end conversions that cost money this will work fine for you and will do perfectly well if you arent sending off to other places, some studios still record at this as well. CDs are only 16 Bit 44.1 so you are not losing any quality. The 24Bit helps with the difference in volume you will get, 24 bit gives you a bit more headroom generally and is easily converted to 16 bit for CD quality.
AVOID MP3s WHEREVER possible in my opinion. For straight Speech they could work fine, but that is about it. When you say audio voice I am not sure wether you meant Vocals for music or Speech? At any rate MP3s are a very lossy format, there are much better compressed formats out there if HD space is a concern(FLAC for example is one of the best compressed formats IMO, and doesnt have the copyright issues that MP3s have, as well as not being a lossy format so you lose no information in it). If you decide to use Audacity I believe it supports Ogg-Vorbis, or at least it does in Linux if it doesnt support FLAC, use that over MP3 as it is a better format, higher quality, and growing in popularity.
If you need the best in free audio software though, switch to linux. Nothing beats Ardour for multitrack if you need that, with Jack, though it is tough to learn both linux and Ardour/Jack at first. Ardour will even give Pro suites a run for their money and is still my product of choice even though I ahve access to things such as ProTools, Cubase, Nuendo etc. If you decide to tackle that post on the linux forums and ill help you out.
If you have other questions though feel free to post them up and Ill answer them as best I can, as will others I am sure.