sometimes its worth trying it with User Account Control turned off. That or try re-installing the launcher alone. It is contained within the 1.4 download, just navigate to program files/electronic arts/bf2142/mods/First Strike and run the program title First Strike Launcher.
Oh, and right click on the launcher installer and press run as admin to install it, then when installed make sure to right click and go run as admin as well to use it 
Oh..btw heres a post I made in another thread when I recently put First Strike on my laptop running Vista home premium 64 bit:
Ok, now got back and fully installed First Strike on my new Vista laptop I can confirm that I can indeed join a server, so for the OP, here is what I did.
Installed 2142 and updated to 1.5
Installed First Strike 1.4
Turned off User Account Control, and then right click on both 2142 and FS icons, then set to run as administrator.
Ran First Strike and allowed it to update
Restarted the First Strike Launcher, then went in to File, Preferences and entered +widescreen 1 in the arguments field.
Ran First Strike, went to options and selected the correct resolution (will show if you enter the +widescreen bit as above.)
Went to online server menu and joined the RSF server.
*note, during the starting of First Strike I had two firewall popups, remember to set permissions for First Strike.
Bite my shiny metal Tie Fighter!

