The things you have to worry about are basically BB and headset. So, use a caliper and make really good measurements of those parts. Then you go to
www.sheldonbrown.com and look at his glossary for threads, bottom bracket, headset, french threads, english threads, bla bla bla and then you will figure out what you have. Also measure fork and frame dropouts with a steel ruler.
After that, roam ebay 'til you find someone who got ALOT of NOS bike stuff to sell, (combine shipping is saving ALOT of money) and then find a groupset you like and buy it. Some parts you will probably have to hunt for a bit longer but you will have plenty to do with the parts you get fast.
When it comes to group sets, Dura Ace is nice, but Ultegra is alot cheaper and if you move back a couple of years then you can get NOS really good Ultegra stuff. Atleast the derailleurs, sprockets and hubs should be NOS. When it comes to sprockets, try friends bikes and see what combination you want back there.
You will encounter questions, and it is good to have a bike maintenance book, but look at those sites also,
www.sheldonbrown.com ,
www.parktool.com , I dont remember Jobst Brands site but it should be a link from Sheldon Brown, otherwise just google for Jobst Brand. He is really good also.
So, good luck mate. And remember, you can always post a question here
