I have a Dell Inspiron 8000 with a ATI M4 Mobility Rage video card, and let me tell you that finding a distrobution of linux that supports this hardware is not an easy task; And the ones that do support my video rarely support everything else (eg. My PCMCIA cards, netgear MA401 WLAN & a Xircom all-in-one)

Mandrake & Redhat support my hardware, but, I despise those two (Horrible systems, just terrible)
Gentoo likes my video card just fine, but has a known bug with the yenta_socket drivers, so I'm forced to use a stage3 (automated) install, which isn't nice.
Debian Sarge, Woody & Patato all hate my video cards. To date I've not gotten anything but WOODY Vanilla boot to even go past the boot loader when installing from CD.

Even BSD distrobutions have problems with my hardware, specifically my video and USB.

This is where Knoppix has seperated itself from all those distrobutions; I've been using knoppix for several months now and have only encountered one situation on any computer i've used it on where it failed to detect hardware (A very, very, very old PCI Ethernet card I slapped into my Gateway 455mhz)

I have been using the knoppix hdd install very successfully for a number of months now. Only problems I've faced are neverending amounts of user error on my part.

I've also had much luck USING knoppix to install other distrobutions. For instance, when I installed Gentoo on one of my desktops, I simply used knoppix to chroot and install when gentoo failed to recognize some of my hardware.

If you have limited harddrive space, I'd go with a basic install of debian (You might also try installing DamnSmallLinux. Never used it, though.) If you have hardware problems like I do, then look into the step I just mentioned, using knoppix to install the other distrobution.

PS. If you plan to use knoppix hdd install, watchout for apt-get update! Knoppix has it's own configuration files for boot up, and debian likes to create new ones where it thinks they should go. Happened to me, And I'm STILL cleaning up the mess debian made.