"Would deleting the 2nd partition (drive D) of my ThinkPad's 30-gig TravelStar HDD automatically de-partition the drive and give drive C a full 30GB capacity?"

No. Drive C would stay the same size.

"I was planning to set up a dual boot with Win2K and WinXP each in a 15-gig partition. But since I've installed MS Visual Studio.NET with WinXP on drive C, I already have less than 6 gigs of space on that partition. After expanding drive C to 30GB, I might keep Win2K on my 10-gig drive and use it as an external usb drive with only MS Visual C++.NET on it, since the complete Visual Studio uses so much more space."

You may be unhappy with that setup...

"To give drive C and WinXP the full 30-gig capacity of my internal drive, would I only have to remove the 2nd partition, or do I have to remove all partitions, re-format and re-install instead?"

Or go get Partition Magic?

Since I do some pre Visual Studio.Net (I have Visual Studio...) Why Windows 2000? While I do have 2000 Pro on the laptop to show off the works, XP Pro is what I use on thw work machine.

I've found this setup to be ideal in that I get to "know" all the files needed for the projects. If the project doesn't build or work on the laptop, then everytime it was some file or item I forget in my export/import routine. So far, it has not been an OS issue.