Sony vegas lagging like hell..

Is it normal that when I add an avidemo200 clip to the timeline and try to view it its pretty much impossible to see whats happening? I have to replay the clip like 8 times (which is really annoying) so that I can sync effects and stuff,and when I add any kind of effect I have to do the replaying all over again :[ So is this what every moviemaker experiences at creating movies or is it just my pc? (my specs btw : amd5600+,2gbram,gf250gts).
If I add a frapsed video there isnt any lag (however if I try the 0.25timescale and 120fps @ vdub method it lags again).
If thats normal,then maybe there is a way to reduce the preview quality in vegas somehow? (ye I tried using Draft (the worst) viewing mode but that didnt help at all).