If you are hard of seeing or blind it may not be sufficient just to increase the text size or using screen magnifiers. What you may need is software that will read out the text on a webpage to you through your computer's speakers. Mac OS X 10.4 and above has this function built in, but for Windows you will need to download special software.
Windows Screen Readers
Browsealoud is free downloadable software that will read webpages out loud for you. Also available for Mac OS X. JAWS is a popular professional screen reading software, and as such is also quite expensive. Window-Eyes is another professional screen reader which also has support for braille displays.
Mac OS X Built-in Screen Reader
From the Apple menu: select System Preferences > Universal Access > Seeing
Here you can activate VoiceOver (also called Spoken Interface on older versions) which will read out text to you through your computer speakers. VoiceOver which comes with Mac OS X 10.4 and above is a fully functional screen reader, just as good as the professional ones you would normally have to pay for.