I am looking for a device that will enable me to wirelessly link a
computer with my TV and Hifi.  The device should have the provision to
browse media from a television menu screen so that I don?t have to
travel to the computer every time I wish to play something.  I have
searched extensively for this and found that most of the devices use
popular wifi based connections.  The problem with popular wifi
connections is that they don?t use soundcard output, thus meaning that
sound from analogue tape decks etc connected through my soundcard will
not be wirelessly transmitted to my Hifi.  I understand that analogue
equipment connected in this way will not have the option of being
remotely selected from a TV screen; however I am happy to manually
play this from the computer as long as the sound will be wirelessly
transmitted to my Hifi (I still want the option to remotely select
digital video and audio files stored on my computer from my
television).

The only product I have found that will fulfill this requirement is
x10 entertainment anywhere -
http://www.x10.com/entertainment/vk57a_s_ps49.html   Entertainment
anywhere uses soundcard output and ships with special software to
enable me to select digital media from my television that is located
on my computer.  The problem is that X10 only ship to the USA as their
product incompatible with UK electricity mains.  Does anyone know of
an equivalent product in the UK?  The only other devices I have found
that use soundcard output are passive devices that simply beam audio
and video from my computer with no TV menu option to select media
stored on the computer.  I can?t stop thinking that there must be
other devices similar to X10 that are available outside the USA
(preferably with S video input).

I think such a device does not exist or would fit the bill.
I would like to suggest getting a mac mini and use it to power your TV (DVI) 
This way you can get a decent browsing experience, you can also play
videos and photos from there as a bonus (think picture frame) .
Finally if your computer runs Itunes, you can share the music and have
your mac mini connect to it for mp3 files. Just use the built in
Itunes music sharing. The Mac Mini has built in wireless so that is
sorted.
You will either need an adhoc wireless connection or just use a wireless AP.

I have something like your set up already. I have an old compaq laptop
running XP Pro. It is connected to my TV via s-video and connected to
my amp via the laptop 3.5mm headphone jack to phono connection in the
amp. It has a 802.11g wireless network card which connect it to my
desktop (thee on that holds all my music/films).
I have also changed the "theme" of the laptop desktop so that it
doesn't look like windows (these are free and everywhere).

Or why not get something like this
http://www.dabs.com/ProductView.aspx?Quicklinx=338Y&CategorySelectedId=11228&PageMode=1.

Good luck.

Rgds,

Stevie

Thanks for your reply but I was looking for a truly wireless solution
that can use my soundcard output instead of just streaming media files
held on my pc through my network card.  There are lots of wireless
media streamers on the market but few appear to use soundcard output. 
As I said this is important as I have analogue tape players etc linked
to my soundcard.  As I said the only device that I can find to do this
is the X10 entertainment anywhere.  All the other devices that use
soundcard output are passive devices.