Have a D600 myself and found anothe post that worked for me!
First, my problem was replying to emails the cursor would jump when typing usually back up into the middle of the text somewhere.
If this is similar, read on.
First, go to Dell's website, downlaod the latest driver for the Alps Touchpad: http://support.dell.com/support/downloads/download.aspx?c=us&l=en&s=gen&releaseid=R113813&SystemID=LAT_PNT_PM_D600&servicetag=&os=WW1&osl=en&deviceid=2514&devlib=0&typecnt=0&vercnt=7&catid=-1&impid=-1&formatcnt=1&libid=17&fileid=149404
Download the driver but do not install yet. Note, this is for a Dell Latitude D600, Windows XP. Vista may have a different driver.
Open Control Panel/Mouse/TouchPad Tab/Touch Sensitivity Button. Open Touch Sensitivity, adjust below the halfway point on the slider. Try different settings, you may also want to check the "Tap off when typing" box.
If you do not show these properties as above, you probably don't have the latest driver installed. In that case, install the driver you downloaded above then come back and refer to the instructions.
I spend 90% of my day on this D600 and really love it, not a speed demon, but light enought to carry with one hand and is a great email/browser machine as you probably already know!
Before installing tis driver