I am on OPT and in 2007 I spent nearly $3400 in medical bills .
Where can I include all those expenses?

1040 Schedule A - but you can deduct only those medical and dental expenses that exceed 7.5% of your adjusted gross income.

See the instructions for Schedule A: http://www.irs.gov/pub/irs-pdf/i1040sa.pdf

You cannot deduct medical expenses on nonresident tax return.