Matthias,
Every controller that I have seen will allow different size drives for Stripe sets. Raid 1,3,and 5 maybe alittle different between different controllers.
Chasim,
In the BIOS for the controller you will tell it to use your 36gb drive and your 74gb drive in a RAID 0 Stripe set. That will give you 110GB of space, you will be using both drives completely. When you are installing your system, if this a new install, you can create your partitions how ever you want an install on whatever partition you want. If this is going into an existing system just use whatever program you like to create your partitions how ever you would like them created. Also if this is a new install and it is for Windows you will most likely need to press F6 to install drivers for the RAID device. They can be found on the driver disk or the website of the controller. It should have an oemsetup.inf file on the disk.