FYI for anyone who might struggle with this issue as I did yesterday.
After reading many blogs/articles and following everything in
http://support.microsoft.com/kb/914277 I still could not connect
remotely to SQL Server Express on my development laptop while I had no
trouble with an identically configured instance of Developer edition on
another PC. Both were fairly fresh installs of XP SP2.

I had even enabled SQL Browser even though I was using TCPIP only and a
static port, which I confirmed was listening with netstat. I also
disabled Windows Firewall.

My resolution finally came when I decided to try simple stuff, which of
course I should have tried much sooner. Alas, I could not map a share on
that laptop. Hmmm. Ping didn't work either. ?!?!? After spending a while
trying to ping between various machines and checking network properties
I discovered the AT&T VPN client I had to install to connect to a
customer's network had loaded a firewall that I didn't know about. I was
pissed it was installed without my knowledge (it would have been one
thing if it was active only while the VPN was, but....).

So if you follow http://support.microsoft.com/kb/914277 and it doesn't
work, start with the simple things first like pinging or connecting to a
share on the PC in question. You may have an unknown firewall ready to
cause you hours of frustration.

--

Sincerely,
Michael Ray
Topshot Systems LLC