|As long as the E521 is a "normal" case that accepts standard power supplies, a Corsair is a good choice.|
Your 300W (or 325W) may even be sufficient...it depends on which video card you're considering. For instance, you should have no problem running a Radeon HD4670 w/GDDR3 or Geforce GT 240 w/GDDR5.
When a video card manufacturer recommends a certain wattage power supply, you should be aware that the wattage figure is for the entire system WITH the card, not just for the card alone. The important factor is the +12v rail amperage & how it's distributed. Many card manufacturers are now making recommendations such as "minimum 400W with +12v current rating of 24A" while others will recommend "400W or greater power".