AirTunes / Airport Express / Windows XP not working together

Here's the issue. I have two PCs available to me; a laptop from work that is tightly locked down by our paranoid IT dept, and a family desktop that has the iTunes library within it. I purchased airport express so that I could stream to my stereo. The laptop does not have iTunes on it, the IT dept having cunningly deployed some way of blocking its install. They did not, however, block airport utility.

Both computers connect happily over wireless to Verizon FiOs and on into the wider world.

1) The laptop's airport utility will happily locate and allow configuration of the express unit.

2) The desktop unit, however, does not find the airport express at all finding no apple wireless devices. However, knowing from the laptop (and from direct to the fios router's network map utility) I can tell airport utility to "configure other" supplying the express' IP address and p/w. Then it finds it and can configure away until I hit the update button. It then can find it no longer until I configure other again.

The point is, iTunes / air Tunes, hosted on the same desktop, displays, I suspect, similar behavior. It never finds the "speakers".

I have tried switching off Norton's firewall altogether, the windows firewall altogether, going w/o any WEP or WPA without luck. Also, I have tried configuring the unit as first as a "joining an existing wireless network", and, second, as it own new wireless network again without avail.

I have spent 4 hrs with Apple support and we thought we had it licked; the speakers appeared briefly after switching to a "bridge" connection share mode. The speakers duly showed up. Letting the gentleman go off the phone in triumph, I stupidly neglected to test the connection from iTunes through to the amp and ran into the error code 15000. Trying some of the ideas in these and other forums to beat that then led me back to square one, never seeing the much anticipated speakers again.

Any ideas out there?

Thanks much!