HP does not list any drivers
for Win 7, but they do for XP. Thus HP does not support Vista/Win 7 on this model so you are stuck using the generic RealTek drivers. Without HP drivers you may never get the front panel jacks to work on this model.
I do a lot of support on the Dell users forum and we see this frequently with older PC's that were upgraded to Win 7 but there are no Dell drivers, as only XP is supported. On desktop systems, the most common "fix" is for users to install a new sound card that is Win 7 compatible. However, on older Dell systems, a proprietary (and undocumented) front panel connection is used so the front panel headphone and mic jacks cannot be used.