Both are HP's!
The one is probably a Pavilion and the other is a Vectra.
Pavilion = personal home computer
Vectra = business/corporate computer
Generally speaking, the Vectra would be better built, run better with full optimizations (better stability), use higher quality components, run NT/W2K/XP.
The Pavilion would be equal to the typical Dell/Gateway/etc.
Similar would be the comparison between the Compaq Pissareo and the Compaq Prolina. Just looking inside the 2 computers will make you question that they both built by the same company.

(Prolina is the business model)
Harder