From manufacturer's site driver support is available upto Vista 64 bit edition.
If it can take vista x64 means, it will work fine with Win 7 also.
Vista drivers should do fine with Win7
http://support.dell.com/support/downloads/driverslist.aspx?c=us&cs=28&l=en&s=dfb&ServiceTag=&SystemID=LATITUDE%20D620&os=WW1&osl=en&catid=&impid=