I sometimes had troubles Trueimage/System not recognizing external drive and during windows-start (XP in this case)system hanged.
For the latter-under certain circumstances when changing settings, when external drive is on during start it will hang. Shut down external drive and system will slow start. It needs a bit of patience.
A) Booting from CD
a1) Bootsequence-change in Cmos
a2) bootmenue used during start.
B1) Whatever change had been during before starting backup to external drive best is shutting down PC and wait a bit before restarting.
External drive is OFF.
B2 )Start PC and start also external drive.
CD can be mounted already or can be done after start but after External drive has been started.
C) depending setting CD will boot or bootmenue will be used.
Alway observe if also second external drive will be displayed. It would be wise to know which type.
If its too quick to observe one can use pause/break-button to stop the start, restarting by pressing any key.

D) With trueimage its important to know:
Free version always needs at least one drive being Western Digital.
Full version can be used with any Drive-brands.
NB: contacts must be clean. use alcohol on brush/I use fresh toothbrush/ for cleaning