I run an ATI HD5870 2GB so perhaps that's a bit overkill for STO.
I'm not sure if the 3450 will run it at max, Fremen, but it's up to you if you want that or just a big improvement on what you've got.
Some one might be able to shed more light on this, but I'm sure I read somewhere that STO isn't that great with ATI cards. Mine runs just fine mind you, a bit hot maybe.
Perhaps take a look at some Nvidia cards for running STO instead.
EDIT: just googled STO ATI cards and it looks like the problem for some was with dynamic lighting, which has apparently just been fixed by ATI in their latest patch, so I think you're good to go with whatever card you select.