I'm installing a 160 gig hard drive. I want to put the OS on one partition and data on another. Any suggestions as to what size to make the partition for the OS would be greatly appreciated.

At least 7, preferably 10-15.

I made the mistake of putting 5GB, for my OS partition, its not that bad but its 3Gb filled up and its still new.

Since you have 160GB, you might want to consider 20GB for your operating sytem, and also breaking up the 140 left into more manageable chunks (this really helps for defragging, for example, or for putting all back up files together, or for searching for something as long as you are consistent in what you put in each partition).
Regards,
John

Thanks for the responses. One more question. Should I put my programs on a different partition?

If I may add my two cents, I have All of my OS related stuff on my OS partition (Antiviral, AntiSpy, Office Apps), then i have games and such on other partitions. One partition (I have 5) is just for MP3s. So it's kinda up to you.

I always keep the OS and my applications on the same partition for marginally better performance and ease of installing updates, etc..
Cheers,
John

Set up is telling me I need almost 1 Gig to set up XP. Do I make the OP partition after installing?
Thanks
Rich

Planning partitions is part logic and part personal preferences. In some cases, partitioning is just a form of filing preferences.

I keep Windows and most-critical apps in my OS partition. I define critical as software firewall, resident AV scanner, resident anti-spyware scanner and resident anti-trojan apps. I keep the OS partition lean, since I image the OS partition weekly to DVD media.

Less-critical apps are installed in my APPS partition. I can't perceive any difference in startup time for program started from the APPS partition and apps started from the OS partition.

I keep all critical data on a dedicated DATA partition, which is imaged weekly to DVD media. Apps such as MS Word and MS Excel are configured to automatically save data files to folders on my DATA partition. I also save some backup copies of critical drivers and program-installs in the DATA partition.

Games are certainly not critical - I install them to a dedicated partion.

Other partitions, BACKUP for temporary isos, and DOWNLOAD for downloads are just personal preference for filing organization.

There are some other valid considerations, for example it's faster to defrag my 8GB OS partition prior to imaging than to defrag an entire single-partion HD.

I've never sensed any performance benefit for using a dedicated page-file partition - but that's almost a religious argument for some.

Thanks to evertone, you have been a big help. I am slipsreaming Service pack 2 into old XP install disk. Big project for a novice but I think I have it figured out.
Rich

This guy, google 'Radified', has a lot to say about partitions. don't forget about FAT/NTFS. Large FAT parts have large cluster sizes but NTFS all use the same size, and they're more stable.