How large to make OS (Vista) partition on partitioned drive?

I've got this new Notebook PC with an 80GB hard drive and I want to partition the drive. OS=Vista Home Premium. Vista allows resizing partitions to some extent.

The drive initially had a Recovery partition that was about 8.8GB. Some background info: I had tried creating Recovery disks from the Recovery partition. That did not work. I called HP and they sent a Recovery DVD to me. I deleted the recovery partition and then tried to "shrink" partition C but it would only let me shrink the C, which was now the full 80GB, by the amount that was previously used for the Recovery partition. I found some reference on the Internet about the resizing/shrinking procedure but was unable to make it do what I wanted.

I decided to use the Recovery DVD to restore the system and then try resizing partition C. BTW, I had called HP "support" before doing this to ask whether the restore procedure would let me partition the drive. They said it would but such an option never appeared during the restore; once it started, I had no options; I could only allow it to run it's course. After the restore, I also noticed that the Recovery partition was also restored, although it is now 6.57GB instead of 8.8. I thought perhaps the Recovery DVD would not put the Recovery partition back; I mean, why have it when I have the Recovery DVD? This time, shrinking worked; it would allow me to make about 45GB of C available to add extended partitions. If I used shrink to the max, I'd have about 24GB for C, about 10GB more than the space used after the recent restore.

24GB might be sufficient, although I'm thinking about making it somewhere between 25GB and 28GB. I plan on installing Office 2003 and that would be the biggest program I anticipate installing; an eventual upgrade to Office 2007 might occur. I'll be installing two or three adware/spyware cleanup tools, CCleaner, and probably a third-party firewall, but these are not fairly small programs. Might be installing the Creative Media Organizer software that came with my mp3 player and probably one or more photo/image editing programs, perhaps an HTML editor and FTP software, and possibly an accounting program such as QuickBooks.

I plan on removing Norton Internet Security Suite and some stuff HP puts on new computers such as HP Games. In other words, some space will be freed by such removals.

Basically, I'm thinking 28GB should be large enough for C. If necessary, I could install some programs on another partition (yet to be created) but I doubt it would be necessary. I also plan on moving standard folders such as Documents, Pictures, and Music to a partition other than C.

So, what say any of thee on the size of C? Anyone with a major difference in perspective on this?