Yeah, this is kind of a known XP thing, sometimes being as craptacular as it can be. Anyhow, try this... it involves the registry so be DAMN careful, backup the registry first and dont touch anything else not listed!! Anyhow, goto this registry key (start, run regedit):
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Class\{4D36E96A-E325-11CE-BFC1-08002BE10318}\0000
then create a DWORD called 'EnableUDMA66' and set its value to '1' (means turned on). If you have that there already and it shows a value of '0' then set it at '1'.