Unofficial, unsupported troubleshooting page for Windows Vista 32-bit and Windows Vista 64-bit.

Getting ArmA to run properly on Vista

Install all updates available from Windows Update
Install DirectX9/10 Redistributable (Links: Guru3d)
Install one of the latest ATI or Nvidia drivers available (Links ATI NVIDIA Guru3d
Install Vista pre-sp1 hotfixes 940105, 936710, 936710, 938194 and 938979
Adjust ArmA shortcut to include -maxmem=512

Known Issues and Resolutions

Until either Bohemia Interactive, Microsoft or the Video Card producers come up with a solution, you can workaround this problem by limiting your System Memory to 3GB by a simple change of settings and a reboot:
- Press windowskey+R, and run msconfig
- At the boot tab, pick advanced options and put maximum memory to 3072
- Reboot
- You can also revert the setting by above method to get your full 4GB back
More methods might be listed soon, together with a method to get a selection screen at system boot up to pick "Normal Operation" and "Limited to 3GB"
More info on boot parameters available below, in the section Related Links

This is a problem confirmed with X-Fi cards and their drivers. Driver Release 2.15.0002 resolves this issue. Or you can add the startup parameter -dsound to ArmA Shortcut but other weird sound problems might arise in that case.

Make sure you have adjusted your startup shortcut to include -maxmem=512, in some cases it might be nececairy to tweak it further back. Try 384.

Make sure your Windows Firewall allows ArmA.exe
Make sure that (if installed) other firewall applications allow ArmA.exe access
Make sure that your router/modem also allows ArmA's outgoing UDP ports towards the internet