Thanks.
Elements 7, being the current version, would support the 450D RAW files; however, I use CS4 and LR2 with my RAW files so cannot say how good PSE is or isn't.
The other option is to convert the RAW files to DNG with the latest free DNG Converter and then use CS2 with the DNGs.
If you have a dual or quad-core system with at least 2GB of memory, I'd suggest using Lightroom.
Read this Adobe TechNote. It answer all ACR file opening questions:_
<http://kb.adobe.com/selfservice/viewContent.do?externalId=kb407110&sliceId=2>