Sip in Windows Live Messenger

I have just installed Windows Live Messenger and was hoping to connect it to
my exisitng SIP account. I seem to have to go into a dialogue with
Microsofts preferred sip supplier. I don't need two 'sip addresses. Is there
anyway in or do I go and see if Yahoo offers the option

Windows Live Messenger 8.x does not support SIP. If you're looking for SIP support you'll
need to use Windows Messenger 5.x:
http://microsoft.com/downloads/detai...f-9157a3b3d774

Yahoo Messenger doesn't either.

We are testing using windows messenger using SIP addresses within our office.
For some reason, when I log on my contacts can see that I am logged on, but
they show as being offline. We have already checked to make sure that they
are showing online. I am at a remote office, but am connected to the internal
network, so all protocols should be passing across the line. Any help would
be appreciated.

I had issues running Messenger from a Win7 hosted - XP Mode VM where I was
able to log on, but all the contacts showed up as being offline. I'm not
sure if I showed up being online or not... What I ended up determining is
that the issue had to deal with the IP address when I was running under. By
default XM Mode uses NAT to piggyback off of the host machines IP address.
As soon as I changed the settings over in the VM to use the host NIC directly
(so the VM got it's own IP address), all of my contacts showed up as being
online. You might check the IP settings for your machine.