I read something similar to your problem on gizmo's freeware site (Microsoft Releases Vista SP2
Poster also had a Dell XPS m1530 which failed to install SP2 (he was not specific about the error codes, although he mentions its similar to the "vLite problem"). He apparently did a "repair install" of Vista after which he successfully installed SP2.
I 'm not sure what a repair install entails both in terms of doing one or what it does, but it seems to me a way to fix some of the corrupted/unreadable files that may be preventing your SP2 install.
I don't if this will solve your problem, but hopefully, this points you in the right direction.