I don’t think eating meat will make THAT big of difference, but it’s better to eat it than to obstain from it, from a general nutritional standpoint.
If you’re going to remain a vegetarian, you might find this plant-based Omega-3 DHA useful: http://www.pangeaveg.com/cgi-bin/miva?Merchant2/merchant.mv+Screen=PROD&Store_Code=Pangea&Product_Code=642
Most other plant-based sources of Omega-3 are made out of ALA acid AFAIK, which your body has to go through the trouble of converting into DHA and EPA.