How can I record at 24bit using Windows XP? Direct Sound?
Audacity no longer supports Windows XP, but you could try using WDM/KS with Audacity 2.0.0, if your XP machine has SSE2 and your sound card drivers support WDM/KS.
Note that the WDM/KS drivers for some old sound cards were buggy and could cause BSOD.