you can get pro tools free, cool edit, sound forge. you can lay down an instrumental on any of those programs then record your vocals on a separate track. i use cool edit, its a good program, i took a snap to give you an idea of what it looks like
http://home.attbi.com/~fplus/ce2.jpg
you can lay down your instrumental then record your vocals then edit. your going to need more than just a good sound card to get best quality vocal recordings, im not heavily experienced in that area but i know just having a good soundcard isnt gonna do the trick. i do record my friends vocals once in awhile, he brings over a behringer mixing board, mic preamp, mic condensor. we set it up in my closet then surround the closet walls with blankets, we use a metal iron with pantyhos as a windscreen for the mic. we do it raw and grimey, how much are you looking to spend twister?