The following usually works on both Tiger and Leopard:
(First, if yours is an Intel Mac, check that Safari is not running in Rosetta, which is enough to slow it to a crawl.)
Many, including me, have had success with adding DNS codes to their Network Settings, with good results in terms of speed-up:
Open System Preferences/Network. Double click on your connection type, or select it in the drop-down menu. Click on TCP/IP and in the box marked 'DNS Servers' enter the following two numbers:
208.67.222.222
208.67.220.220
Click on Apply Now and close the window.
Restart Safari, and repair permissions.
If that didn't do it, then try this as well:
Empty Safari's cache (from the Safari menu), then close Safari.
Go to Home/Library/Safari and delete the following files:
form values
download.plist
Then go to Home/Library/Preferences and delete
com.apple.Safari.plist
Repair permissions (in Disk Utility).
Start up Safari again, and things should have improved.
Less likely, but possible, is that the slowness is caused by a Trojan such as the one called 'DNSChanger' or 'OSZ.RSPlug', which can alter the DNS settings of your network connection. .
If you have agreed to that installation, your system can be infected and your DNS settings altered, which results in your system using the wrong DNS servers, which can slow web surfing to a crawl.
This can be fixed by downloading and running a freeware utility called DNSChanger Removal Tool which you can download from here:
http://www.versiontracker.com/dyn/moreinfo/macosx/33696
Once you have run that utility you have to re-boot your Mac, then reset Safari, and re-enter your DNS settings in System Preferences/Network.
