Pretty cool, I remember seeing your post of that thing on the Retro Rig Thread when I was a lurker here, I too have a Dell Dimension 4300S with a matching setup, it was my main 9x gaming machine until it went on hiatus due to a mishap from ordering the wrong USB front hub board (never use a front hub board from a GX280 on a GX240).
The erratic behavior caused by the GX280 front hub on each OS I've tossed on it ATM:
Windows 98SE: has a slower startup time, and the busy cursor shows for a minute afterwards.
Windows 2000: shows the "Safely eject and remove hardware" icon on the taskbar the whole time.
Windows XP (RTM): shows a flashing "USB device not recognized" icon on the taskbar - had to disable USB in the BIOS to make it go away.
Before it was using a semi-functional front hub from my decommissioned GX260, it didn't fit in the case due to it being from a Mini-tower while the GX280 hub was from an SFF desktop. maybe if I replaced it with a hub from an SFF GX240 or GX260 it would work properly again but I'm kinda tight on money ATM so I'll get back to it eventually.
I'm surprised at how upgraded that machine is, it's nothing like the one I have. I suppose if you swapped out the 512MB GF6200 with an older Low-Profile AGP card with less VRAM you could setup a dual-boot with XP and 98SE/ME to have a fast 9x gaming rig.