For IE, the simplest way is to hold CTRL while using the middle scroll wheel on the mouse to adjust the font size. This works for me in FireFox, as well. However, this may not always work depending on how the font is coded. If CSS (cascading style sheets) was used to format the font, for example, the middle wheel method doesn't work. But in that case, it probably wouldn't matter anyways because the font should be fixed regardless of most other settings.
Also, if your problem is with programs *other than* an internet browser, we're probably talking about a different kind of settings issue. So this is a critical point: Are you experiencing issues *only* with your internet browser, or with *other* programs as well?
If you experience font issues with *more* than just IE: I believe there is a DPI setting which affects font sizes; perhaps somebody else can expound on this. This is something to look into.
But to be honest ... If you experience the problem with windows programs in general, I would just use a restore point to revert the settings to their prior configuration. That's almost like cheating, because you didn't really get at the problem, but it gets the job done.
That is, if it's not a hardware/driver issue. I've had problems where my video card was going bad and my computer would automatically adjust the video settings to accomodate descreased performance. (1) I either needed a new video card, or (2) I needed to simply update the video driver.
In your case, it sounds like a weird settings issue, not a hardware/driver issue, because usually a driver or hardware failure results in *everything* looking bigger - but you mentioned that some things look smaller. The real mystery is how these settings were changed ... sounds like a strange thing for a virus to do, but you might want to check just in case (and frequent scans are good anyways). Or perhaps a recently user-installed program affected some of your settings (although, this again sounds like a strange thing for a program to do). Might there be small children adjusting your settings just for fun? (I did that as a child, heh)
First, try the CTRL+ScrollWheel solution. Otherwise, I think the simplest solution - *if you have issues with many programs, not just IE* - would be to use a restore point. You won't lose any files, and your computer should look the way it did before the issue occured. Make sure your video drivers are updated. And lastly, keep us posted.