It is not surprising that Avast4.8 still works with WinXP. As I said in my very first post, Avast4.8 still works with Win2K. Win2K and WinXP are NT technology operating systems.
Win98 is a DOS operating system. WinME is also basically a DOS operating system. Avast4.8 stopped working for these two.
My guess is the difference between handling Outlook and handling the Avast virus database is that the OS has to deal with a larger chunk of the database at any instant. Then you get the ‘out of storage…’ error. Another guess is that it is related to heap size. It doesn’t matter the size of the Swapfile or how much Vache is reduced.