Downgrade MediaPlayer in Win XP – WMP6.4

How do I downgrade Windows MediaPlayer to an earlier version (i.e. V6.4) under Windows XP?

Specifically, the version of one of the .dlls used by WMP7.x plays .mpg (MPEG1) files jerkily or erratically. If we try to replace this in C:\Windows\System32 with an earlier version, XP merely re-installs the later version. Can we “turn off”/work around this auto-recovery by XP ?

TIA
Kelvin