I suppose you have read the SuSE installation manuals thoroughly? You can lose all your data unless you know what you are doing. After reading SuSE manuals you could go to
www.tldp.org whenever you need to know something. It's a good place to start.
1. No linux installer will convert the filesystem from anything to anything. They will simply delete the partition and create a new (ext2/3, reiserfs) system on it. If the new partition you are talking about is /dev/hda2 or /dev/hda5 then most likely you have lost all your data. Unless, of course you did a defragmentation in Windows beforehand and SuSE resized either one of your partitions during install.
2. ATI cards can be made to work in four different ways: the opensource ATI and RADEON drivers, proprietary ATI (Radeon) driver (from
www.ati.com) and in framebuffer mode. I'm familiar with first three. First try to manually force SuSE to use the opensource RADEON driver. If it does not work, try the framebuffer driver. If that does not work, get your hands on proprietary ati drivers and install them. Read all the howto's related to the last mentioned - they are not really that easy to install, without X, anyways.
I can't help you with your AVANCHE soundcard. Try
www.google.com/linux and see what pops up. Most likely they are either unsupported, or use a kernel module that is not loaded automatically.
3. Usually DHCP is used to resolve your IP address and stuff. If internet connection was ok in windows, then you should have no problems in Linux, either. By default, even WIndows uses DHCP.