You can either download the standalone NetDraw installation package, or download the UCINET installation package, which includes NetDraw. The NetDraw installation package will uninstall any old version you have (but keep your data files), install the new one, and add it to your Start menu.
Alternatively, you could download and install UCINET, which will automatically installs NetDraw.
Note that if you want to run netdraw from ucinet, you may have to go to Options|Helper applications in UCINET and tell it where you have installed netdraw.
For information on changes in NetDraw over time, see the versions page.