windows software raid 0 volume extremely slow

i have two identical 120 Gb HDDs. each is connected as master to a separate ide channel. among other ide devices is only a cd rom drive connected as slave to secondary channel. but i almost never actually use it so it shouldnt be affecting the issue with the HDDs.

both of them are set up as dynamic disks. each has a simple volume on it and a 100Gb chunk that is a part of a striped volume set up across these two disks (using 1 such chunk on each of the drives). so far so good. this configuration i suppose is acceptable according to windows help instructions.

right after installing windows i measured performance of all of the three volumes. i used winbench99 and transfer speeds were pretty close to what one would expect from such a seemingly nice configuration. simple volume showed about 56MB/s which is just 2MB/s below technical specifications for this model. striped volume showed 82 MB/s speed.

but here's what i get in real life from these disks. copying/moving from simple to simple volume gives me speed of about 23MB/s which is far from 56 in the test but ok i can live with it. what's most outrageous is the speed of the striped volume. all copying/moving operations involving this volume are at speed of approximately 1.5MB/s. what kind of fast volume is it? in fact its the bottleneck in my system right now- - i can't even watch a divx movie from it without getting the slideshow effect if i simultaneously say copy something onto this volume or process some file on it or do smth like that. copying a 700Mb movie from/onto it takes up to 10 min. this IS ridiculous.

i have measured the performance of these disks again thru winbench right now it still shows the same good speeds of 56 and 82 MB/s respectively. what is it - windows using the available bandwidth incorrectly/ineffectively or what?

and it's not a problem of these specific drives. before them i had two other drives and pretty much the same sort of configuration and had exactly the same situation with them: perfect results in winbech (exactly up to expectations) and on the other hand lousiest performance (1.5MB/s for raid 0) with real tasks.

i really need to figure out what is wrong here cos i'm planning to upgrade to 3x200Gb disks and right now i dont have the slightest inclination to use the "magical" software raid 0 again.

system config: msi 6378 v.3 (via kle133 w/int. vga), athlon XP 2400+, 512 RAM, winxp