Vector shapes -jagged pixel fill

Hello!
This issue has been bothering me for some time now and I'm hoping it's just a simple fix. I'm using version CS4 and am on a Mac.

Okay, a few months ago Photoshop started acting a little strangely or I'd just never noticed before. When I use the custom shape tool any line that is not either perfectly vertical or perfectly horizontal will be jagged along a pixel grid. The path, when visible is perfectly smooth but the fill is not.

The images I've been testing on are set to 300dpi. If you need more information please let me know and I'll pass it along as best as I can.

I'm sorry if I'm not languaging this correctly but I lack some essential PS vocabulary. Similarly I'm not sure how to post the screen shot I took to this thread. I'm not a programmer, just a guy who likes to do design projects for fun so please keep your responses on the dumbed-down side of thing.
Thank you in advance, this will help me immensely!!!

this is how PS operates, it's not a vector program like Illustrator. Your paths/shapes are defined as vectors but then PS has to fill them in as best it can using pixels.