No knowledge about the Dell Inspiron 5150 specifically to offer. Do you need the pcmcia support? If not you could disable it with a "cheat-code" and that might help. (If you think you need it for something like a wireless card you might research that a bit, you might not be able to use your specific pcmcia card anyway for other reasons.) As to the overheating, I see this even under Windows on my desktop while booting Windows. After booting Windows settles down, but Knoppix may not have power management in it for your particular chip set (again, don't know about the Dell Inspiron 5150 but I know it doesn't support power management properly for my HP ze4210). In my case my notebook runs hot and eats battery but does not overheat; maybe you will be OK if you can get past the boot hang.

I think the cheat-code that might help is nopcmcia, but you might want to follow the documentation link at the top of the page and check me on that. You may need others also to get fully booted (I need a combination of 2 codes before the notebook would boot with recent Knoppix versions, took me six months to find the right combination (it wasn't my highest priority)).