There are no special requirements to run the Redline TimeAttacks, but they do want you to have some seat time in PDX/HPDE programs because the passing is fairly open and it is a more competitive enviroment.
There is also the Club Trials and Time Trials program via the SCCA which for some reason we wont put on here (level 2 and 3 events, with the PDX program being level 1). For level 2 you dont need much more than what you would have prepped for autoX, level 3 starts requireing more safety and liscencing prep.
NASA also offers HPDE's and a time attack program but I do not know much about them.
So all in all, start out with some PDX's (we've got a few coming up later this month) or some HPDE's offered by the various other car clubs in the area.
Terec