I navigate with my mouse but this is not working fine because it reacts very sluggishly. Is this normal or are there better navigate-options?
I'm using the following hardware
* Pentium, Ubuntu Hardy, corded mouse and keyboard
It's pretty slow on windows as well which is why it's quicker using a keyboard
Pentium? What video hardware and are accelerated drivers installed? I haven't had issue with mouse performance but I usually use a remote...
Most skins don't handle a mouse well. It's likely large images trying to load quickly that's causing the "sluggish" feeling. TBH, a mouse is an awful means of navigating a media center and XBMC was never really designed to be used with one.
If you have LCD TV chances are great that it's the TV that is the source to your problem.
The TV's contains various picture enhancement features (100Hz, PixelPlus etc etc etc) On some sets this can quite quite high latency. (as for my set I have like 120ms with everything turned on)
Turn off all picture enchancement features on the set and see if things get better.