If im understanding you corretly you want to get rid of linux and keep windows. If true grab a livecd or use the mandrake rescue cd if there is one dont know, you can try sys rescue cd. Anyhow at the command line you can use a program called cfdisk, or qtparted/gparted if it is included. Delete the partition that contains linux. Now to get the boot manager to work i dont know of way to do this with a win98 cd, because the boot files used for xp and 98 are vastly different. What you need more than likely is a regular cd not to install. While windows is loading or when done loading hit r (repair) a dos prompt is presented type in fixmbr this will reinstall the windows xp boot loader.
Option 2 bypass the linux livecd just do the windows install cd and fixmbr, then in windows start>settings>control panel>administrative tools>computer management>disk manager you should see something along the lines of unrecognized partition format.
At this point after the mandrake partition is wiped you have one of two options and im not following exactly you want done.
A. If you have xp pro you can convert the drive to a dynamic partitiona and add the free space back to xp.
B. Create a spare partition to hold data so if windows crashes you wont lose all data.
C. Leave the partition blank and install your flavor of linux.
I have no idea if this is what you want, either way hope this helps somewhat.
This is the link to sysrescue cd, this includes graphical partitioning tools.
http://www.sysresccd.org/Main_Page