No discussion on pirated stuff here... Go original.. Since you can afford an apple product a windows license shouldnt be too much problem right? I would suggest windows 7 through bootcamp...

Actally 64GB is much better for him as he has 4GB and 32 cant fully utilises the RAM... Just bear in mind that not all software supports 64 bit.. So make sure you find out all those softwares you use are 64 bit available and compatible before installing...

Bootcamp wont make your mac laggy as its run completely on windows using all the resources. So your processor/graphic card/RAM are all solely used by windows in bootcamp if you log into windows... 4GB RAM should be enough

Bootcamp is easy to setup as long as you have your windows CD... Just follow through the guidelines and you are good to go..

Furthermore you could also use it to play games =)... Not really a bad thing... Just have to restart everytime you wanna switch to windows OS =)

Actually dual booting is very beneficial but mostly and mainly is for gaming compared to other usage... Other usage can be performed using Parallel Desktop/VMWare as they can run parallel with Mac OSX... Of course they are extra costs =)... Boot camp is free as long as you have a windows license =)

Yes parallel will share resources for the RAM/Processor/graphic with Mac OSX and definitely will slow down if you run those memory intensive programs..

Yea Autocad has 3D and processor does play a part for Autocad... Basically GC and Processors are important if you are doing those mentioned... Faster processor = more computing power = faster calculation etc... Better GV = better graphic, sharper etc..