If you have any difficulty in creating WD lifeguard DOS version CD i recommend downloading "Ultimate Boot CD". It is a fairly large download (500 + MB) but a very handy boot CD with all the tools you need to diagnose a PC or laptop.
Download address : http://www.ultimatebootcd.com/download.html
Burn the ISO using Imgburn. You can find WD test tool under "HDD-->Diagnostics" menu. There are also other tools to test the overall health of your system.
Be sure not to select "write zeros" in the lifeguard tool as it will permanently destroy your data. Run a full surface scan only.