I have an old reliable Dell PC still running win98sePlenty of memory and two HD's.To good to scrap :) How do I install Windows 7 and keep the old win98 just in case ...

You could always image the machine; however, Win 98SE? That is like going for a jog in the mountains of Pakistan in nothing but running shorts waving an American flag: sooner or later you are going to get burned.

Well W7 uses NTFS instead of FAT32 which cannot be read by W98 & W7 and vice versa so you will have to either create a partition & format it NTFS (formatting can be done during the install process of W7) or dedicate an entire drive for the installation. None of the data on the NTFS partition/drive can be read (or even seen) by W98 (if you take an entire drive for W7 then you can't even detect the drive).Remember to keep the minimum specs in mind.1Gb memory20Gb HDD1Ghz processor minimum.