Welcome to the forums. The process while it might seem difficult, is actually quite easy. First and foremost, you must unlock your TP to flash any roms. Secondly, you dont have to backup your stock rom, the stock roms are located in a sticky at the top of the forum.
to unlock your phone, follow the steps in the first post of this thread:
http://forum.ppcgeeks.com/showthread.php?t=69854
as for roms, nobody can tell you which one to use. I personally use Mightyrom 4 which is a winmo 6.1 base (same as stock rom but tweaked), along with a long list of other tweaks and cabs. regardless of whether you want winmo 6.1 or 6.5, there is a rom to suit your needs, and i recommend you read the chefs comments about each rom, and view the screenshots to get a better idea of the look and feel before you flash.
Typically the procedure is as follows. download the rom package, which will be either a .zip, or .exe. if its a .zip, open the .zip and folders and look for a file called romupdateutility.exe, which you run and follow the onscreen instructions. If its a .exe, simply launch it and follow the instructions.
Keep in mind, the above is a generalization of the process. Follow the unlocking tutorial above, and the specific roms instructions for best results.
Also keep in mind, many roms are simplified down to work on multiple carriers, so some carrier specific items such as sprint picturemail will not be included. search the forums and you will find the answers you are looking for in regards to these items. Good luck and happy flashing.