Have you applied a market fix?
I know I was having this problem with SetCPU, it would say downloading for days after putting on Froyo, but never download, and never show up in the notification bar. The way I got it to quit FCing finally when I hit "Cancel Download is I opened the Market, clicked the Menu button, then Downloads. When I found the offending app in the list of downloads, I long pressed it, and this came up with a sub menu which allowed me to cancel the download. When I then went to the app info page in the market, it downloaded just fine and installed just fine. Try it.