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It's been working fine under 32-bit, but I've now installed it on v.1218 of XP Pro x64. HL2 loads OK, I see the Valve man and the text screen, then it crashes back to desktop with an error that available memory is less than 128MB! Obviously this isn't the case, there is well over 3GB free, so I'm suspecting that it's related to XP x64 showing applications a much larger address space e.g. After Effects has 3.5 GB to play with.