Hi Bilo,
1st, indeed, check your partition structure using fdisk /status switch (for safety) as Wizbones recommended (you can also do it from start -> run -> fdisk/status)
Now, I've also checked on mandrake & it has an option to install OS directly from Windows 95 or 98, you've better to select this option, because it doesn't reconfigure your partition structure (MBR actually) and probably better for beginners.
There are many programs for creating/resizing/deleting partitions without damaging the data, I personally prefer PQMagic but it's not shareware

(since v2.0)
I assume there is such a shareware or freeware utility.
I'm almost sure there is an option to modify your HDD structure during installation of mandrake, but it's usually complicated with linux (Disk Druid was just a headache for newbie like me

.
I'm don't know about mandrake, but you probably would have to create separate partition for linux and also swap drive ???
Cheers
Chef
p.s. Make sure to backup all important data before starting the installation of new OS.