Tascam us 1641 midi latency

[Imaginator]

Hello everyone,
i just bought a us 1641 usb interface and the problem is that when i record in nuendo(ver 3.2), i have latency, only to the recorded midi.There is no latency at all to the sound i play with my korg x50 as midi controller
The ammount of latency can vary from small to huge.
I use the latest drivers/firmware from tascam
I googled for this problem and i found two solutions.One was to enable use system timestamp in the device setup and the other solution was to find a file called "ignoreportfilter", then cut it out and paste it one level up in the Nuendo root folder.
Both helped temporarily, i mean for a few minutes.After two or three small recording attempts, latency was growing bigger and bigger...
Any suggestions?

my system is
2.4 Ghz intel core duo 2 (6600)
ram 2Gb
motherboard Asus P5Q Deluxe

i use windows xp pro sp2