The MTR states that players are barred by policy from entering a PTQ if they have already won one that season. How does this affect PPTQ's? That is, if I win a PTQ, can I participate in PPTQ's or RPTQ's that season? If I win a PPTQ or RPTQ, can I participate in PTQ's that season?

The MTR is not the best document for this information. The document you should be looking at is the MTG Premier Event Invitation Policy guide. This has the information on participant eligibility for PPTQ's and other premier tournaments.

http://wpn.wizards.com/sites/wpn/files/attachements/mtg_peip-14_14oct31_en.pdf

Thanks for the link, Cris, and you're correct, that's a good resource.

David, I think your answers are all in the PEIP, primarily sections 13-15. If you have a player who isn't certain about eligibility, they should probably contact Wizards' Customer Service.

I want to remind others about Forum Protocol, specifically not answering questions like this one, unless you're an Official source. (Note the link at the top of each Forum web page; read it; profit.)

d:^D