Hi rstar009,
On-Screen Keyboard might be easier to use if you change the font used to illustrate the keys on the screen. The fonts that most people find easiest to see on the screen are Verdana and Arial.
1. Open On-Screen Keyboard by clicking the Start button Picture of the Start button, clicking All Programs, clicking Accessories, clicking Ease of Access, and then clicking On-Screen Keyboard.
2. Click the Settings menu, and then click Font.
3. In the Font box, select a font, and then click OK
Refer the following on how to change the font of on screen keyboard(Also applicable for Windows7) : http://windows.microsoft.com/en-US/windows-vista/Change-the-font-for-On-Screen-Keyboard-keys
If that does little help, as a workaround you may drag the On-Screen keyboard and increase the size, to make the font appear bigger.
However you may not be able to enter the same font in facebook since facebook has a standard font for all and needs some changes in facebook settings
For more clarification on this, you may contact facebook
Azeez Nadeem - Microsoft Support