Here is a new version of portable VNC working with 2.5 FW.
What's new in this version :
+ Compile/Port on latest version of PSPSDK
+ Support >= 2.5 FW
+ Add Support for DHCP (works now with my wifi router)
+ Bug fix (exit hangs) on FW >= 2.5
My contribution on this app is minor (only code rewritting to fit new interface of PSPSDK,
and copy/paste wifi code from psp-ftpd).
I just wanted it to work on my PSP 2.5.
I've not tested it with 2.6, but it should work properly.
Portable VNC is distributed under GNU licence, and sources are provided with the archive.
Hope that helps, :)
edit: here is a new version working also for 1.5FW : pspvnc v1.2.1