Completely Messed Up iTunes Library, Need Help

Hello everyone. Recently I consolidated my music Library and also down-coded everything at 192 kb/s, or at least I thought... Now both iTunes and my iPod will only recognize the files that I had not down-coded. The program I used to recode the files is called Xilisoft Audio Converter. It recoded the files at random bitrates like 190 kb/s, 193kb/s, and 194 kb/s. I dont know why this happened even though in the program I set the recoding settings as AAC and 192kb/s bitrate. I put the files on my iPod with Winamp since iTunes wouldnt recognize them then my iPod wouldnt play the songs. I then viewed the contents in my iPod through iTunes and saw that iTunes was saying their bitrate was variable. Anways, the program I used screwed up the bitrates of all 3700 or so songs that I have spent the passed week recoding. Is there any program I can use to mass convert these files at a guaranteed constant bitrate while keeping the ID3 tags?

EDIT: Winamp is doing the same thing my iPod is doing now. It is just zipping through all of the files I recoded as if they dont even exist.. It attempts to play them but only stays on the song for like a millionth of a second and goes to the next, and then repeats, thus "zipping" through all of the recoded songs. The songs that I hadnt recoded though work fine... Have I lost everything?