Can wooden window wraps be installed after Vinyl windows (like Pella) have already been installed?

yes they can be installed afterwards. but depending on the siding that is being applied there may be an issue there. Is the trim going on top of the siding or is the siding butting to the trim? If its butting to it then the trim needs to go on before the siding for installation ease.

Cost is a question that depends on what you want, and the type of window you are installing. A custom trim set could cost you up to 6-800,00 depending on the type of wood and the trim design.

I just did a job last summer where I was matching some 1900's trim which had a small crown molding on the top and full 5/4 stools, it got pricey wood inside and out ran around 125.00+ (clear yellow pine) and it took about 12 hrs labor to do each window as I was building to match existing.

labor is going to vary depending on where u live

Just remember you get what you pay for in most cases. If you have a GOOD trim man, who knows his business, he's worth every penny. dont let the framing guy just throw something up. the trim can make or break an entire job.

You will be able to do a clean install. The directories Program Files, Documents and Settings, and Windows will be moved to a folder called windows.old and placed on the root of the c: drive. If you ever want to revert to previous OS, you can boot from the Vista DVD into the Windows Recovery Environment (Win RE) and move the files from windows.old to the root of the Drive. Then go into a CMD Prompt and run bootsect type, bootsect /nt52 all . This will bring the PC back to ntldr instead of the new bootmgr.