In file ​http://winswitch.org/dists/lenny/main/binary-i386/Packages, as well as in Packages for other Debian/Ubuntu? versions, xpra is mentioned as a dependency for winswitch, but its description is missing in the mentioned Packages. The package correctly resides in ​http://winswitch.org/dists/lenny/main/binary-i386/xpra-0.0.7.16.i386.deb and after downloading and installing with

dpkg --install xpra-0.0.7.16.i386.deb

the installation of winswitch from the repository succeedes.

Right now it's not possible to install Win Switch in any version Ubuntu. The dependecies say that you need at least xpra xpra 0.0.7.14 but only 0.0.6.0 is available in Ubuntu... YOu can check this by looking into... ​http://packages.ubuntu.com/search?keywords=xpra&searchon=names&suite=all&section=all

If you really need such a new version, you need to offer this version in your repos.

$ wget "http://winswitch.org/dists/gentoo/xpra-0.0.7.17.ebuild"
--2011-01-24 20:47:30--  http://winswitch.org/dists/gentoo/xpra-0.0.7.17.ebuild
Resolving winswitch.org... 194.145.197.105
Connecting to winswitch.org|194.145.197.105|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 566 [text/plain]
Saving to: `xpra-0.0.7.17.ebuild'

100%[======================================>] 566         --.-K/s   in 0s

2011-01-24 20:47:30 (21.6 MB/s) - `xpra-0.0.7.17.ebuild' saved [566/566]

$ ls /usr/local/portage/net-misc/xpra/
Manifest  xpra-0.0.7.16.ebuild
$ sudo cp xpra-0.0.7.17.ebuild /usr/local/portage/net-misc/xpra/
Password:
$ sudo rm -i /usr/local/portage/net-misc/xpra/*16*
rm: remove regular file `/usr/local/portage/net-misc/xpra/xpra-0.0.7.16.ebuild'? y
$ sudo ebuild /usr/local/portage/net-misc/xpra/*ebuild manifest
>>> Downloading 'http://gentoo.virginmedia.com/distfiles/xpra-0.0.7.17.tar.bz2'
--2011-01-24 20:51:46--  http://gentoo.virginmedia.com/distfiles/xpra-0.0.7.17.tar.bz2
Resolving gentoo.virginmedia.com... 194.117.143.69, 194.117.143.70, 194.117.143.71, ...
Connecting to gentoo.virginmedia.com|194.117.143.69|:80... connected.
HTTP request sent, awaiting response... 404 Not Found
2011-01-24 20:51:46 ERROR 404: Not Found.

...
>>> Downloading 'http://windowswitch.org/src/xpra-0.0.7.17.tar.bz2'
--2011-01-24 20:51:47--  http://windowswitch.org/src/xpra-0.0.7.17.tar.bz2
Resolving windowswitch.org... 194.145.197.105
Connecting to windowswitch.org|194.145.197.105|:80... connected.
HTTP request sent, awaiting response... 301 Moved Permanently
Location: http://winswitch.org//src/xpra-0.0.7.17.tar.bz2 [following]
--2011-01-24 20:51:47--  http://winswitch.org//src/xpra-0.0.7.17.tar.bz2
Resolving winswitch.org... 194.145.197.105
Reusing existing connection to windowswitch.org:80.
HTTP request sent, awaiting response... 200 OK
Length: 887754 (867K) [application/x-bzip2]
Saving to: `/usr/portage/distfiles/xpra-0.0.7.17.tar.bz2'

100%[======================================>] 887,754      251K/s   in 3.5s

2011-01-24 20:51:51 (250 KB/s) - `/usr/portage/distfiles/xpra-0.0.7.17.tar.bz2' saved [887754/887754]

>>> Creating Manifest for /usr/local/portage/net-misc/xpra
912 ~ $ sudo emerge -pv xpra

These are the packages that would be merged, in order:

Calculating dependencies... done!

!!! All ebuilds that could satisfy "xpra" have been masked.
!!! One of the following masked packages is required to complete your request:
- net-misc/xpra-0.0.7.17 (masked by: invalid: IUSE contains defaults, but EAPI doesn't allow them)

For more information, see the MASKED PACKAGES section in the emerge
man page or refer to the Gentoo Handbook.

$
$ eix -I portage$ --format '<installedversions:NAMEVERSION>'
sys-apps/portage-2.1.9.25
$