Hi All, the good news is I have finally got it to work on my N73. Its taken 2 days of trial and error. I am getting PMs to help with signing, now that I have figured out how to make it work without the Nokia SDK, its shouldn't be a problem, you just need signsis and that is available in the 1.3mb file I linked to earlier as opposed to the 355mb SDK. For those of you still struggling to figure this out here it is.
Please note, this is seriously non-trivial and it may not work for all configurations. I am using a thinkpad T42P and Widcomm drivers from IBM. The native bluetooth drivers in XP SP2 didn't work for me. I am not using mrouter or a proxy server, analogx for this method. The basic thing is first get gnubox.sis working on your phone for which you need to get it signed. Then configure incoming connections in XP, then configure GNUBOX on the phone and keep your fingers crossed.
STAGE 1 - Sign GNUBOX.sis
1. First get gnubox.sis.
http://rapidshare.com/files/4548686/gnubox_s60v3.sis
2. Then download this file, it has the application Signsis.exe
http://download.macromedia.com/pub/developer/make_sis_explained.zip
3. Get this app from Symbiansigned.com . You will need to sign up for an account here
https://www.symbiansigned.com/DevCertRequest_30_10_2006_v2.0.exe
4. Follow the step by step guide by Lurzsan_07 on page 6 of this thread. Post #88 to sign gnubox.sis. You don't need to download the SDK, Activeperl or Mrouter. Use Signsis.exe from step 2 with the commands given in post #88.
http://www.howardforums.com/showthread.php?t=1003702&page=6&pp=15
STAGE 2 - Configure XP SP2
1. Follow this guide exactly with 2 exceptions:
http://web.singnet.com.sg/~kinston/Bluetooth Internet.htm
a. When setting up the 'Bt' access point in your phone enter your dns address in the 'advanced setting' section. 'For your dns address type 'ipconfig /all' in the windows command line.'
b. In incoming connections under the tab 'Users' tick mark 'Require all users to secure their passwords and data'
Stage 3 - Success!
Troubleshooting help
http://xan.dnsalias.org/gnubox/trouble.html#Node_20
Remove native XP SP2 bluetooth drivers
http://support.microsoft.com/default.aspx?scid=kb;en-us;840635
Do a google search for Widcomm drivers.