I bought a new Ipad, 16gb, 3g, and as my laptop was out for repairs (windows vista), I synced to my old desktop (XP) so I could get the Ipad up and going.

I had used the laptop Itunes to snych my Ipod Touch. When I plugged the Ipad in to my repaired laptop, the message is that you can only synch to one Itunes, and do you want to erase all on the Ipad and add the stuff from the Itunes in the laptop. I have bought apps for the Ipad since I last synched my Ipod Touch to the Itunes. I got no question about transferring my purchases to the laptop. I think I got that question the first time I synced with the old desktop.

Do I have to lose the apps that I added before this second sync?

And, (boring aren't I?) how do I take the old desktop off the number of computers I have added to Itunes? There is a max of 5, and it says I am at 3.

If apps are all you've loaded on the iPad then it's easy.

Just take note of the ones you bought. You can go back to the App Store and re-download them for free, as long as you are using the same iTunes account that your purchased them with.

Music or movies you've purchase on the iPad could be a problem. If you've got some on the iPad that are not already in your iTunes library there will be a few extra hoops to jump through.

Method One
If you share your computer with other people, you can maintain separate user accounts for each person who uses the computer.
This is useful especially if each user has different tastes in music or other media; users can maintain separate,
personalized iTunes libraries and can customize their devices' sync settings accordingly.

Method Two
You may use multiple devices on a computer without the need to create multiple user accounts.
To do this, you can set iTunes to update each device with only certain playlists.
This method allows you to put all your music on, say, your iPod and keep your iPod shuffle
updated with only your workout music. Here's how to do this with iTunes:

Method Three
Create a separate iTunes library for each device. Note: It is important that you make a new iTunes Library file.
Do not just make a copy of your existing iTunes Library file. If iTunes is open, quit it.

Here is the source:
How to use multiple iPods, iPads, or iPhones with one computer

Thank you wise Ipad gurus! I should be able to sort myself and my Ipad/Ipod out with this info.