Vista or any OS is there any restriction on Max C drive space.

I want to know about the C drive

Just thought I'd throw in a nice link to show you how big these hard drives are getting. Right now from what I can see, it looks like they already have plans and are hoping to create a 37.5 Terabyte hard drive.. that's 37,500 Gigabytes of data. Granted a DVD only takes up approximately 8 Gigabytes, that tells you that the sizes on these are huge ^^. Hopefully this link leads you into a bit of interest and understanding on how technology has improved over the years =).
http://www.itwire.com/tech-lifestyle-news/new-products/8350-seagate-to-offer-300-tb-hard-drive-by-2010

My response stays the same bsharath. The C:Drive has no real limitations. The capacity is little under your maximum size of your hard drive (Because of the Master Boot Record and File Tables taking up a little space). If you ran out and bought a 2 Terabyte hard drive, you could set that entire size to one partition (C Drive) if you wish~.

Keep in mind though that if your computer is really old or out-dated, your motherboard may not be able to read the newest types of Harddrives to their full potential. Also if you're using Windows XP instead of Vista like you mentioned, there may be a cap because Windows isn't exactly the best at long-term service. I believe the last thing mentioned about a Partition limit for XP was 1 Terabyte, whereas things like Vista and Windows 7 I believe bypassed that limit and currently can be capped to any type of hard drive we have on the stores today.

Actually, I misspoke there. Some 64 bit versions of Windows will boot from GPT partitions, but not all.
http://en.wikipedia.org/wiki/GUID_Partition_Table#OS_support_of_GPT