On a different note, avoid the purple-green dirt cheap Ebay adapter: you will have no use for the mouse (green) part and it almost always needs a reboot.
I happen to have two of them. They're all over the place in Germany, so if you're unknowing and just buy a PS/2 to USB adapter, you'll most likely get one of these.
My observations: They're crap. The mouse part is incredibly jerky and the keyboard part doesn't support the ISO layout. Which is even more irritating WHEN IT'S SOLD IN GERMANY. Oh, and it doesn't work with Linux.
Sometimes (although this is quite rare) it seems to kinda 'reset' itself - the computer ignores input for a second and the the lights on the keyboard flash on and then off. Then the keyboard comes back into action. I've seen this happen probably less than ten times in over a year, and it's good to go after a second. I've noticed this happen on both my laptop and my desktop, so it was more than likely adaptor related. Don't let it put you off it, I just thought I'd throw it up here for reference.
Awww, crap. I almost thought the Belkin adapter would be a solution.
Apart from the two craptastic adapters I own, I have another one; it features a translucent green case and looks just incredibly fugly (I can supply a photo if you so desire). This one works with Linux and supports the ISO layout; the mouse part doesn't jerk around, but it stops working with my Endurapro after about 5 seconds. I thought it was due to the Endurapro drawing too much current, but even a hacked-together PS/2 extension with usb-powered 5V leads (I know this is not recommended by the USB standard) will not remedy the situation. Also, it has the extremely unnerving "PS/2 reset" problem you described above. In certain circumstances, i.e. heavy pounding or testing for rollover, the thing behaves exactly as mentioned above (the flashing LEDs could indicate a PS/2 reset, but I don't have an oscilloscope, so this is just speculation), which is incredibly unnerving.
Given the extreme abundance of just a few models of adapters on the market, I think Belkin just use the same logic as my adapter, which wouldn't remedy my problem at all. At the moment, I use the translucent green adapter for the keyboard part and the "cheap ebay" adapter for the pointing stick, but it's quite jerky.
I probably wouldn't have gotten the Endurapro if I knew what a pain PS/2 to USB adapters are. Unicomp would sell me a USB Controller for the Endurapro, but the shipping cost will most likely cost me an arm and a leg ...

-huha