How to reinstall windows xp without losing program files

Unfortunately "No"

OK.
You state that you have to reinstall the system a lot.
Due to Registry corruption and so forth.
What is going on with the registry?
What are you doing to the system to cause all these issues?

--
Do you have the Restore Disk?
(or)
Actual Windows XP CD? (OEM or Retail)

--
This is the best way to do this, and one of the biggest reasons why
I always tell people to create multiple partitions on their drives, if they do not already have them done.

Install with the Actual XP CD.
When asked where you want to install.
(List Drive(s))
Delete the C:\ drive.
(If you have 1 massive drive, then)
Create different partitions.
20-50GB for the C:\ is enough space. (20000 - 50000)
Then create other partitions.

OK.
This is the cool part about doing your system this way.
Lets say the following exist?
You have
C:\ (Windows Drive Space)
D:\ (Downloadable program files categorized in their own folders and so forth, not to be used to install to)
E:\ (Used to install programs to, instead of installing into C:\ drive all the time)

Benefits of this type of setup.
If Windows becomes corrupted, then all the programs that are not installed in C:\ drive will be
Saved in the other drive(s) that they are installed in.
ALSO (This is the great part)
When you have to reinstall the system, and you get to the option
Where do you want to install Windows to?
You choose: Existing C:\ drive. [Delete] and [Create] it again.
And NEVER TOUCH the other drive space.)

Most people are against this way of doing the system, and those people are the ones that end up losing more data than they should on a reinstall, even after they keep backups on external media.
They spend hours backing-up data that should already be backed up and it is a mess.
Creating multiple partitions on your drive. Allows you the freedom to do whatever you desire.
Like myself.
C, D, E, F, G, H, I , J, K, L, M, N, O, P, Q, R, S
These are my drives; they are always on 5 different hard drives.
And all drives server their own purpose. Most drives can be taken from my laptop
And connected to another computer and the programs will run from within the drive itself.
Saving all data to itself, NOT on the other system.

Backing up data.
In one of your Partitions, you can create a Folder call it:
Backup\
Within the Backup Folder, you do something like this.
(Replace <Username> with logged in Username)
Backup\<Username>\05-08-2009\
Within that folder, you store all the data that you want to keep from
C:\Documents and Settings\<Username>
Like:
Desktop
My Documents
Favorites
Local Settings\Application Data\Identities\{LONG NUMBER}\Microsoft\Outlook Express
Application Data\Microsoft\Address Book
Application Data\Microsoft\Internet Explorer\Quick Launch

Storing everything within' it actual folders, so you would create that long folder name
And then restore it back once the system is reinstalled.

This will make it a lot easier for you to overcome the loss of Data.
Do normal backups to the Backup\<Username>\05-08-2009\
For that date, and when you reinstall, then you create another folder with another date on it.
Backup\<Username>\10-08-2009\

Anyway;
Sorry for the long breathed information, but this is what I do, and I loss data ONLY when a hard drive crashes, and I keep solid backups continuously.

Good Luck
Carrzkiss