I have just installed a new 320gb IDE hard drive on my 3-year old HP Pavilion PC. I use an external 80gb IDE hd for backup. I am currently using XP Home. I would like to make the 160gb IDE (now replaced by the 320) as backup. My plan is then to use the 80gb USB hard drive to operate Mint 4. The techies I have talked to aren't sure, although one has successfully installed Linux to his Mac but has not set one up on a Windows machine. The principle seems simple enough; dual OS booting is not my first
choice. I am mildly concerned about tinkering with the BIOS. I have
no intention to partition the 80gb. Would someone please refer me to
a definitive source for this process, preferably in Peter Rabbit English.
I tend to go to sleep on the drivel found in--dare I say it--Microsoft
sites. I have found several Linux sites that talk around the subject
but do not spell it out. My simple mind works on the principle of
progressive point form explanations. Alternatively, I have a perfectly
good 80gb hd that will be scrapped and I won't have a Linux OS. HELP.

I don't see why you would use the external harddrive for linux, because it can be alot trickier to use external usb harddrives to boot linux. If you are putting mint on the external drive you have to partition in order to install linux on it, linux normally requires a swap partition(where stuff goes when you run out of ram) and a / partition, which is basically the C:\ drive in windows. I don't understand why you don't want to dual-boot though.
Here is how I would do it
320 gb harddrive
1st partition would be windows
2nd partition would be / for linux
3rd partition would be for swap for linux(around a gig or so)

80 gb drive
I would use this as a data/backup drive

I also don't understand why the 80 gb harddrive will be scrapped, considering you could still use it for data and/or backups