I have been reading about the "1792 configuration change has ocurred" error that I get sometimes when I boot my PC now and it looks like my battery might be loosing it. I have never replaced a battery before. I usually just replace the motherboard or the whole computer (by the time the battery goes there is much better out there anyway). What can I expect to happen? I understand that the BIOS will reset and have to recognise everything again. I won't loose anything on my hard drives, will I?

If you take the battery out and leave it out, the BIOS uses the default configuration settings [as seen in the BIOS Setup].
What you get depends on what the default settings are, but they should be conservative/safe settings that cause no problems.

If you then fit a new/good battery, changes can be made to those defaults and those changes will be retained [won't be retained without the battery].
You may, or may not, want to make changes to the defaults.

Whilst the PC is working well, go into the BIOS Setup and write down a list of all the existing settings.
Then after you've fitted the new battery, check all the new [default settings] against those.

If you study the settings, eventually you might begin to get some idea of what each of them does.

I have a [slightly dated] document explaining typical settings; you can have a copy of it if you like.
It's hosted HERE (http://www.verzend.be/v/8033070/01_04_08_BIOS_Setup.doc.html) until Aug 28th.
Anyone can click on that link and download it.