Here's a site with a lot of info and links, granted it's in the UK, but I've learned a lot about my RSA here.
http://www.porsche964.co.uk/
This is a site I subscribe too, lots of info, great group of guys.
http://uk.groups.yahoo.com/group/porsche964/
The biggest problem about changing the plugs is all the stuff that has to come off to get to them.
Upper plugs, remove air cleaner and fan motor on left side of engine.
Lower plugs, remove undertray, right and left exhaust, and all the heat shields.
Takes longer to remove and install all the stuff in the way than to change the plugs.
Good Luck, Don