This Forum is an absolute infinitive well of information! It's now 4pm and I have just realized that I spent about the past 8 hours reading and browsing. Yikes! *laughs*
So thank you all for sharing your knowledge - I am quite overwhelmed, having gotten questions answered and new questions have arisen.
It will take me weeks, if not months or years to get down the theory. I hope I'll not chicken out from practice when I get there ;c)
Eitherway, knowing from what I did with film fotography and knowing I want to limit a little bit of my gear to a more usable size, I have decided to do the following changes to my gear:
Once the Sigma 70-300mm is here, I will try and sell it - it's the non-APO version and since I own the Canon 75-300mm IS USM lense, I won't really need the SIgma anyways. According to reviews, the Canon does have the better critiques, so I will stick with it.
Also, the Canon 80-200mm MKII I have never really used. And if I won't find a use for it anytime soon, it'll go :c)
FD lenses basically have to go, though I will keep the 17mm, the 50mm and the 100mm - I would want to try the reverse adapter with those in order to shoot macro and with the aperture ring I can still adjust apertures with those even, if I understood right.
I also have plenty of filters, that unfortunately I bought wrongly:
The 49mm ND - Filter for example. I didn't realize, that my 50mm 1.8 needs a 52mm Filter. I had totally forgotten... Shame on me.
I will have to replace it with a 52mm.
Furthermore, I do have the 72mm POL Filter but no lense going with it - so either I find a lense with it (isn't the Canon 17-55mm a 72mm? Or was that the 10-22mm?) - so either, selling off all my leftovers, will make enough to contribute to getting a nice wideangle (I will decide between the Sigma 10-20 and the Canon 10-22 when the time draws close), or I will just have to get rid of the 72mm Pol, too - it's a HAMA btw 
..
Soooo ... If you think, I am making major mistakes here, please correct me 
If you want to swap my 49 ND filter against a 58mm one, feel free to do so ...
Btw, does anyone have experience with a 58mm WideAngle Lense extention?
Up until I saw it in the complete Camera Kit for the 40D, I never even heard of those.
Again, thanks for sharing your knowledge here and I am going to continue browsing tomorrow (after 8 hours in one day, my attention span is quite exhausted and I will return to easier reading - like "Understanding Exposure" and the "D40 Manual" :P )
*** 
