Taget fra fra halflife 2 forum.
1. Remove any old versions of Steam.
2. Download the Steam client.
3. Download PrcView - a freeware utility that displays running processes.
http://www.xmlsp.com/pview/prcview.htm4. Run PrcView.exe. You'll see a list of running processes. Keep this somewhere visible, so you can monitor it and click on it.
5. Run the Steam.exe
6. You'll see Steam.exe listed in Process Viewer as a running process.
7. Watch it closely.
8. Soon, you'll see SteamTmp.exe launch. When you see this launch, immediately Kill the Steam.exe manually.
9. The SteamTmp.exe will close, and then continue running again as Steam.exe (a new Steam.exe not the one you killed in Step 8 above).
10. Continue updating as normal, and close Process Viewer.
11. Everything should be good to go!
Håber du får det til at virke.