If your device is GSM, you can get plenty of ROMs over at XDA:
http://forum.xda-developers.com/forumdisplay.php?f=440. (Who is your cellular provider?) Most newly developed ROMs are using WM 6.5, but a few are still around biult on WM 6.1 if that's what you want to use.
For applications, you can go here:
http://www.freewarepocketpc.net
http://www.pocketpcfreeware.com/en/index.php
http://forum.ppcgeeks.com/forumdisplay.php?f=23
http://forum.xda-developers.com/forumdisplay.php?f=260
and
my 4shared listed in my signature.
With this list, you'll pretty much be able to find anything you could want to do on your phone. To install applications, copy the *.cab to anywhere on your phone, and run it on your phone through Explorer.