I don't know what you have updated, but if it is to Windows XP, here's a clipping from the 'help'

To use ClearType for screen fonts
Open Display in Control Panel.
On the Appearance tab, click Effects.
In the Effects dialog box, select the Use the following method to smooth edges of screen fonts check box.
Click ClearType in the list.
Notes

To open Display, click Start, click Control Panel, and then double-click Display.
ClearType is ideal for portable computer and other flat screen monitors. ClearType may appear slightly blurry on desktop computer monitors.
Whether you select Standard or ClearType from the list, you must have a video card and monitor that support a color setting of at least 256 colors. Best results are achieved with High color (24-bit) or Highest color (32-bit) support. Click the Settings tab to set Color quality.

On the other hand, if you updated Internet Explorer to version 7, you may want to select a better font via Tools/Internet/Fonts and you may have to try a few to find one you like.