I am taking an 8.5x10.5 page of text into a 30" x 20" poster. Should I make the page into a PDF and blow it up. Or should I format the page into 30x20 and then have it printed by a commercial printer?
It depends how your original page of text was created? If it's a Word doc or something like that, just recreate it as it will be minimal time.
If you are using Illustrator / InDesign (or another vector package), just create at the actual size and get it printed by a commercial printer. This will give you more control and make sure you don't have any distortion (as 8.5 x 10.5 does not scale into 30 x 20).
Remember to ask your printer what spec they want the file to be (bleed / crop marks / etc) and to turn all text to outlines (the text created in Word is not outlines).