OK, then. I've done this myself before many times. The process seems lengthy, but it is not difficult. The Windows upgrade will not disturb the Ubuntu partition, as Ubuntu uses a totally different file system that I don't think even Windows 7 can read.
First step is to perform any backups that you can. If you have enough space on an external hard drive or extra partition to back up everything, great; if you don't, then just backup the files that are the most important to you. If at all possible, at least back up the file /boot/grub/menu.lst from your Ubuntu installation.
If you have a fast Internet connection, Windows Live SkyDrive provides 25 GB of online storage (individual files can be up to 50 MB), so you might be able to use that for backup if necessary as well.
Once you have backed up everything that you can, you're ready to begin the upgrade. Now, everyone on these forums (including me) will recommend a clean/custom install over an upgrade, but the choice is yours. If you do a clean install, just make sure you select the right drive and partition for it, and you'll be fine.
There is a chance that Windows might not even disturb the GRUB bootloader with an upgrade. If it leaves GRUB alone, you don't have to do anything. However, if GRUB is overwritten and no longer appears, you should be able to restore GRUB to the Master Boot Record by booting to the Ubuntu 8.10 Live CD.
Once you are in the Ubuntu Live environment, load up the terminal and enter
It should return a location in the form (hd#,#). Then enter
where the numbers match the ones returned by the "find" command. Finally, enter
Now GRUB should be reinstalled to the Master Boot Record. Now reboot (taking out the Live CD) and boot into your Ubuntu 8.10 installation. Replace the /boot/grub/menu.lst file with the one from your backup. You should now have GRUB as your primary bootloader, with an option to boot into Windows from GRUB. If for some reason there is still no entry for Windows in GRUB, there are MANY guides on how to add Windows to GRUB manually available on the Internet (Google).
Let me know if you have any questions, or if you need further explanation.