Ah.... Now I've got a handle on you. Ditch the stock app
This problem is more common than it should be with it. Even though I've seen it occur with handcent, I think you'll find that app enumerably better than the stock version. As a matter of fact, I completely removed the stock messenger app...but we're not going to get into that here.
Let me walk you through finding it in the market. I'm going to assume that you obviously searched for it by typing in 'handcent' so we'll skip that step for both our sakes.
Are you running a stock phone? What ROM are you using, you can find this by going into your phone's settings, scrolling to the bottom, and touching 'about phone'. Tell me the ROM version, and the Kernel version.
Either way, go into your phone's setting, then into your applications. If your running Froyo touch all at the top, if your running 2.1 touch the menu softkey, and set the filter to show all. Scroll down until you see the market, touch that. Then clear data, clear cache (if thats available), force close.
Power off your phone.
Pull the battery out.
Count to 5.
Put the battery back in and power it back up. Wait for it to load, go the market, and try searching for handcent again.
If it still doesn't show up, then try searching other words like "text" or "SMS"
Post back, if this doesn't work, I've got a few more tricks up my sleeve
