Certainly taking physics before the OAT can help, but the concepts they test are actually pretty simple. The calculations are easy (no calculators, remember) you just have to know what you're doing. I went through undergrad in a weird way, so my physics courses were pretty much long forgotten by the time I got around to taking the OAT. I studied some MCAT prep material, an OAT question booklet, and went over the basic stuff from a physics text. It ended up going really well.