not only audacity but there is another program which is also free called krystal which is pretty good, you might want to try them both out and see which you like better(they both have the same capabilites for the most part just differnt interfaces and work in different ways)
if you dont mind paying some a used m audio delta 2496 off ebay for about 60 bucks then a used dmp3 for for about 50 and then a used studio projects b1 for about 60 as well. if you can find these deals you are looking at 170 for a really solid setup that will definately have a good soudn for acoustic and vocals (new this would be 350 but looking on ebay those items appear to be going for aroudn those prices)