A single universal XP image is not likely possible as long as there
are needs for mutilple HAL types. Sysprep images are still limited
by HAL's - so with a Sysprep'd image, you will need one for each HAL
in use. Remember that modern processor architectures such as
HyperThreading processors complicate the landscape to some degree.
RIS in Server 2003 can do HAL "filtering" and unattended installs
still provide correct HAL detection, but both RIS & unattended
installs are significantly slower than typical "image" technologies. There
are stated workarounds available using the major imaging
product suites from Symantec, Acronis, & Altiris, as well as now in
SMS 2003 w/OSD Feature Pack. Single image solutions typically
require significant creative scripting using SMBIOS recognition code
as well as "just in time" driver & HAL selection.
List your specific Dell & HP models, the imaging tools that you use,
and people on this forum will probably be able to assist with their
own creative solutions.