DramMeister, all the best scenery is in the west!
Zulumika, I suggest you start by spending several hours browsing through the Undiscovered Scotland site (
http://www.undiscoveredscotland.co.uk). Now let's narrow it down:
Do you want to visit distilleries? How many? Do you have a favorite?
You want to see castles? Atmospheric ruins, or stately homes?
How interested in history are you? Archeology? There are some amazing sites--stone circles, chambered cairns, etc.
I'm afraid I've given Glasgow short shrift in all my visits, as I find Edinburgh far more attractive, but I'm sure someone here will argue with me. (For your sake, I hope they do.) But I think it worthwhile to start with a couple days in Edinburgh. It's a little tricky, but see if you can get there from the airport in Glasgow without a car. Visit the castle and the Royal Mile, and at least take a run through the museum for an overview of the country's history.
Then head north. There are a lot of attractions in the south, in the Borders and in Dumfries & Galloway, but I think the Highlands are what most people want to see.
You can see a lot in three weeks. The trick is to find a balance between moving and settling. Three nights in any one place gives you two full days to explore it. If you're going to spend a week in one spot, you'll want to be sure that it's a good spot.
B&B's are the way to go in my mind. They offer a good way to meet local people and fellow travelers, although you shouldn't be surprised to find many of them being run by English incomers!
I always push Orkney, because I think it is an awesome place. But if you go there, you will want three full days at the very least.
I don't know about staying in a castle...I can't afford that stuff! But look in the back pages of Scotland Magazine (WM's sister publication) for listings of upscale accommodation.
Here's a twenty-day sample itinerary:
1. Edinburgh
2. Edinburgh
3. Craigellachie (Speyside)
4. Craigellachie
5. Craigellachie
6. Inverness
7. Inverness
8. Plockton
9. Plockton
10. Skye
11. Skye
12. Skye
13. Fort William
14. Glencoe
15. Islay
16. Islay
17. Islay
18. Inveraray
19. Glasgow
20. Glasgow
That's just off the top of my head. Do some research, come back with more questions. You'll have a great trip!