When I edit the ~/.vendetta/config.ini and set windowmode=1 I get this error when starting up vendetta:

X Error of failed request: BadValue (integer parameter out of range for operation)
Major opcode of failed request: 135 (XFree86-VidModeExtension)
Minor opcode of failed request: 10 (XF86VidModeSwitchToMode)
Value in failed request: 0x3200002
Serial number of failed request: 38
Current serial number in output stream: 39

System:
Portage 2.0.51-r8 (default-linux/x86/2004.2, gcc-3.3.3, glibc-2.3.4.20041102-r0, 2.6.9-gentoo-r10 i686)
=================================================================
System uname: 2.6.9-gentoo-r10 i686 AMD Athlon(tm) XP 1800+
Gentoo Base System version 1.6.8
Python: dev-lang/python-2.3.4 [2.3.4 (#1, Dec 2 2004, 02:20:09)]
distcc 2.18.3 i686-pc-linux-gnu (protocols 1 and 2) (default port 3632) [enabled]

X is the Xorg server:
X Window System Version 6.8.1.901 (6.8.2 RC 1)

Nvidia driver 1.0.6629

One of these days I need to try out the Xorg server. It seems to have a problem with the VidModeExtension.

If you're in window mode, it probably shouldn't be calling SwitchToMode, but it does just to switch it to the default mode.

Hmm, that may be the problem. Xorg may not use mode 0 as the default mode, and I assume that to be the case, so that's probably the cause of the BadValue.

This should be fixed in the next patch (later tonight).

Whoa!
install rc2 instead, x11-base/xorg-x11-6.8.1.902

it works for me (tm) and is no longer exhibiting such problems like the "crash on leave vendetta"

Ah, nifty. So they fixed their stupid extension. :P