|An important consideration here is the Dell PSU. In the Vostro 230 Mini Tower, it's only rated at 250W.|
Will this be sufficient for the Radeon HD 5450.
The Radeon spec's suggest a 400W PSU is required. Could be that's a tad overcautious, as tests suggest it's no power guzzler, but feeding it with a 250W PSU leaves little if any headroom.