how should i
 

i still only got windows, but im thinking of getting Slakware or Mandrake.
but i want to have windows at my computer at the same time.
im woundering how i should do it, if i should splitt my 40 gb 10000 rpm
in two partisjons or i shuld install it on my 120 gb 7400 rpm harddisk.
will linux affect windows in any way?

Do anybody have any suggestions?

(i know my english is bad, and this may sound stupid.:p)

Hi,
Welcome to LQ,

If you have a spare disk, i would suggest you use the other hard drive. That way you can keep windoze away and avoid potential problems.

Mine is setup that way :D

I would also suggest you search in this forum as there are hundreds of threads regarding installation.

It really doesn't matter so much. Most of the partitioning depends how much space you want for linux and how much you want for windows. If you are new to linux I would recommend Mandrake over Slacware. I would recommend putting windows on all of the 120gig and then splitting the 40gig. On the first half of the 40gig install linux and make the second half of the drive windows FAT32 instead of NTFS. This is because linux can read/write FAT32 but only read NTFS. This way you can easily share files between the two operating systems.