slow hd-performance

hi all,
I've a new computer (dual xeonIV, 1 gb) with xp-prof;
the load of xp and start of applications is very fast (I use adaptec
and ultra-160 hdd's).
if I select in the explorer a file and doubleclick or rightmouse-click
the systems make a pause round about 20-25 sec and after this
the application with the selected file (pdf or doc or else other)
starts in a second. the pulldownmenue makes a pause with the same
20-25sec, too.
there isn't a virus-scanner on the system, and no trojaner or else!
I've installed the sp1 and hotfixes and ie6.sp1 and so on, the newest
adaptec-driver and so on! tested all drives with chkdsk and
TimeStampInterval = 0.....

have anyone a tip to solve this??? TIA


:-) thomas, germany

slow hd-performance