I'm preparing the new partitioning of my laptop, so I would like to know how much space are going to take a full installation of this development environment.
Long time ago has elapsed since my last installation of a full Visual Studio environment, so my guesses are that these days the minimum space needed will be around 15 GB.
The answer depends on whether the partition needs to hold data, too. How large will the databases be that you intend to create, and what is the number and size of your Visual Studio projects? What languages do you want to install, what SDKs will you install? Do you need the full MSDN library?
If you plan to do real work, allocate 50GB at least, better 100GB. There is a lot of stuff that accumulates.
I run my main server with a small bootable partition, it has XP, VS2008, SQL 2005 plus a few other tools and it comes it at 11G.