A few things to look into:
1. Try running the RoM client in Windows 7 or Vista compatibility mode. Windows 8 is rather new, I do not have it installed (and won't--I don't care for the interface at all), and there may be a compatibility issue with it. You can also try running the RoM client in Win XP compatibility mode, but I've personally
never had an issue with it and either Vista or Windows 7.
2. If you're using an nVidia-provided video driver...don't. Dell has this tendency to use semi-proprietary ("custom") video chipsets in the video cards they install in their computers. You'll need to use a video driver for your card that's supplied by Dell, not from nVidia.
3. If you want to try the slim client--which is no longer available through Gameforge or the mirror download sites--you can go here:
http://forum.us.runesofmagic.com/showthread.php?t=70835 Inferiority was kind enough to set up downloads for both the slim and full clients in the links in that message thread.
Also, when installing either client,
temporarily disable your a/v and firewall programs. Do the install, run the client so it will update itself, then re-enable the programs after it's completely updated.