A whole lot of misconceptions. I think the problem is definitely driver-software related, either that or its the placebo effect
I would definitely install the IAA drivers (should be on the Dell disc), as it improves IDE performance by a long shot. It also depends on application. Also remember to defrag your drive (even if it is a new install). If your applications are not multithreaded, or you will never use multithreaded applications, then go to the BIOS and turn off HT. HT can incur a slight performance penalty when activated with applications that are not multithreaded (a rather serious loss to ancient fortran applications, i might add, but thats DP in general).
Benchmarking tools: I'd give the ZDNet Winbench (or whatever), SysMark office, Content Creation stuff a try. You'd have to look for similar test setups elsewhere as a reference.
I suspect that the Seagate Barracuda ATA V is part of the reason your new system feels unresponsive... they have pretty slow seek times. If you can live with 18Gb of space, a Cheetah 15k.3 or a Fujitsu MAS-series would light a fire under it, guaranteed. edit: of course there are 36Gb and 73Gb models too, but the 18Gb is about at most peoples' pain threshold, at $200-210
ATA V is slower than the faster HDDs. If your previous system had SCSI or say a WD JB, BB series or 180GXP, it would account for the loss of responsiveness.
Way wrong answer
Dell is the problem.
Never seen one that was what I would consider speedy. Even the precision workstations with SCSI suck..
The computer can only be as good as the person operating it. I suppose all the PowerEdge racks in my company's lab serving an entire ISP are a figment of my imagination. They only suck if the person using it sucks. There are people in my area that have a $5K Precision workstation running 50 processes at the same time and wondering why its slow.
A hard drive with an 8mb cache would also help out.
My IBM 15K RPM U160 drive has 4MB cache, and I can assure you it blows the crap out of any WD JB 8MB cache or WD Raptor 8MB cache drives, or even those 16MB cache almighty notebook drives. Cache is overrated, its like the Mhz myth... more correlates to better, but more doesnt mean better.