For what it's worth, I'm in the midst of planning my own first trip to Scotland (with 3 buddies) for the last part of summer '06. I'm planning an itinerary very similar, with first 3 - 4 days in the St. Andrews/Edinburgh area, followed by 3 - 4 days in the Dornoch area.
I came across a fellow named Allan Ferguson who helps plan trips to Scotland, and has just released the third edition of his book "Golf in Scotland". His services and his book were well recommended to me by others on this site. I just received the book on Saturday, and it appears to be a wealth of valuable information. All types of practical tips (take a couple of bungee cords to strap your bag to the trolley) as well as "Eight Ways to Get on the Old Course". In my eyes, it was well worth the $25 purchase price, and can be ordered directly off his website.
Courses that my group are looking at playing include The Old Course, the New Course, Lundin Links, Leven Links, Elie, Royal Dornoch (both courses), Tain, Nairn and Brora. We won't be able to play all of these, and there are some other courses still to be discussed, but these are the ones currently under consideration. We would really like to play Machrihanish, but haven't yet figured out how we can fit it in with our timeframe and travel plans.