See if any of these adjustments work for you. Some of them are for Vista, and some are for IE8:
1. DPI - Right click on Desktop, Personalize, On Personalization Page, go to left column to: Adjust Font size – DPI, DPI Scaling: Click on Large scale (120 DPI), and click Apply.
2. At the lower right hand corner of every IE web page, there’s a Zoom control that lets you increase the size of every web page, and it stays at that Zoom setting for every page. I keep mine at 125%.
3. Open Internet Explorer, go to Tools, Internet Options, General, Accessibility, Select Ignore font styles specified on web pages, check boxes and click OK, then Apply, then OK.
4. Open Internet Explorer, go to Tools, Internet Options, Advanced, uncheck all three:
Reset text size to Medium for new windows and tabs, and
Reset text size to Medium while Zooming, and
Reset Zoom level to 100% for new windows and tabs
5. Open Internet Explorer, click the Page button, click Text Size, and then select the size you want i.e. Large (Largest may be too large).
6. Ease of Access Center – Go to: Control Panel, and Explore all settings. Under the following heading, Make things on the screen larger, select: Change the size of text + icons. This takes you to the dpi settings screen.
7. If you have a scroll wheel on your mouse, use command/ctrl + your scroll on a web page to increase the font size.
8. Magnifier – For those instances when you need to magnify a certain portion of the screen - go to Start, in the Search pane, type in "magnifier" + click the program at the top. (To read more about Magnifier go to Start, click "Help & Support" on the right hand side, type in "magnifier.") Magnifier is actually located at: Start, All Programs, Accessories, Ease of Access, Magnifier.