Welcome to LQ Divider.
Whether you are going to get rid of windows altogether or make it share the HDD with linux, your installation cds have the necessary tools to change the HDD partitioning for your setup. If you are going to leave windows on it, do take the precaution of defragmenting before you resize the windows partition (supposing you need to in order to create space for the linux partitions (I'd suggest you make a minumum of two partitions, one called 'root' or '/' for your actual linux system (take about 10G if you are going to do a full Suse install) and another called '/home' for your personal files. If you want to share files between linux and windows your safest option is creating a FAT32 partition for sharing as NTFS isn't fully suppoted.
For questions about whether software originally designed for windows will work in linux with wine, check the Wine DataBase (
http://appdb.winehq.org/)
As far as virus are concerned, you should only be concerned about that if your linux box is going to be a gateway to windows machines, since viruses will not affect the second, but still pass on to the others.