What version of Illustrator do you have?
The infinity symbol is found in most fonts, and the easiest way to find it is to use the Character Map. (Go to your Windows Start Menu>All Programs>Accessories>System Tools>Character Map.) I'm not sure if there is a Mac equivalent?
Scroll through the Arial font, and you will find the infinity symbol about two thirds of the way down. Copy the character and paste it into your illustrator file.
NOTE! This will only work in Illustrator CS! This latest version of illustrator uses a new text engine that is much more functional than the old one. (For more info, read this post about the new text engine in the Adobe Illustrator Forum
.) Illustrator 10 does not appear to support the infinity symbol as a text element and it will appear as a question mark.
Once you have the symbol in the illustrator file, you can keep it as text, or you can make it into a compound path by right clicking on the text box and selecting "Create Outlines." This then lets you select the anchor points and move them around - play with the text a little.
If you wanted to practice making symbols, you could trace around the outside of the infinity symbol using the 'pen tool' and the 'convert anchor point tool'.
Let me know if you have Illustrator 10 and I can send you a file with a compound path version of the infinity symbol in it.
Hope this helps,