Poor performance on MBP 2.53 Core2Duo

I didn't partition my MBP hard drive and installed FCP X onto my system HD. I'm am getting real poor performance in a SD project with DV footage. I am getting drop frames on playback sometimes and I tried the background noise removal on a clip and it drop frames every time I use the slider.

Any thoughts? I'm on a MBP 2.53 Core2Duo, 4GB RAM. DV footage at 29.97.

Thanks!