Again, what are the numbers on the Enermax PSU? The ones that are on the side of the PSU and look like this:

Specifically, the DC output amperage numbers. Looking at this Enermax 300W PSU above, however, if yours is similar, you should be fine. Unplug all the lights in the case though, just to be sure.
How would I do that anyway? the only CD I have is the Emachine restore CD.
Ouch.

THAT is why I will never buy a branded machine, no matter HOW good it is - you never get a copy of an operating system, you only get a "restore" disk. Blech. AFAIK, you can't install windows on a new system using a proprietary "recovery" disk.
At any rate, I'm still a little confused....
You have an 80 GB HD and a 10-ish GB HD, the 80 GB has E-machines XP-home, and the 10 GB HD has Win98? And you have NO "bare" operating system disks?
It sounds like you have two drives with two different operating systems, and niether one has the ability to boot on the new Motherboard. At this point, I'd attempt to borrow someone's spare HD and install/boot from it, AFTER obtaining a copy of WinXP the OS, not the recovery disk. You can get a copy for less than a hundred bucks at Newegg by buying any old hardware item (even if its only a 5 dollar cable) or you can find someone who works at Microsoft who can get you their Employee price from the company store. (25 bucks for Home, 30 bucks for Pro) And no, I don't work for them, I work for Boeing.

Once you've installed/booted the borrowed drive, copy all the pertinent info onto it from the other HDs and then wipe them, and repeat the installation procedure.
I.e.
borrowed drive = drive 1
80 GB drive = drive 2
10GB Drive = drive 3
Clean install on Drive 1 as master, drive 2 as slave.
Hook up Drive 1, copy all necessary info from 2 to 1.
Hook up Drive 2 as master, drive 1 as slave, wipe and clean install on drive 2, copy data from drive 1 to drive 2. Remove drive 1, install drive 3 as slave. (obvious, but shut down power between drive swapping).
At any rate, it looks like you are stuck at the moment, without a bootable copy of an OS (either bootable CD Rom version of XP or floppy boot/Win98 CD).
BB