How much HDD space should I give Windows + these apps?

I just got a job as a web developer and programmer. I need to be able to use Visual Studio and Photoshop on my personal PC so I can learn how to use them well enough for work. I've decided that I'm going to run Windows XP (since I get it for free from my school, and it is probably smaller than Vista) in a VM and install the programs onto that.

The problem is this: I have limited hdd space. Right now I have 25 gigs free on my internal HDD. If I give Windows 15 gigs of that (leaving me with 10 for Linux), do you think that will be sufficient? Not only will I have to install WinXP, but I'll also have to install all the updates, Visual Studio, Photoshop, and perhaps some other utility programs or maybe even some additional development programs. What would you do in this situation?