Yes, you sure can replace the front plate. You mean the touch screen?
Take a look at the excellent ifixit guide here:
[guide|6052]
I would go for the complete screen assembly with the frame. That simplifies the installation and you get a nice new frame also. Get it here:
[product|IF132-001]
Or you can also get them even cheaper on Ebay. But I would be sure the part is of good quality like the ones they sell on ifixit.
Here is an example of a pick from Ebay:
http://cgi.ebay.com/iPod-Touch-1st-Gen-1-Front-Screen-Digitizer-w-Frame-/160632122193?pt=Other_MP3_Player_Accessories&hash=item25666bab51