I would try e-mailing Aspire with your boards dimensions and mounting hole locations, if your board has any. Maybe send them some pictures with some measurements.
you're most likely better off getting a new motherboard. dell tends to use non standard dimension motherboards and cases because they can. they also use proprietary power supply so the power supply you get will need to either be modded or get a convertor.
Although the non-standard PSU was true in systems from around 96-99, that is no longer the case. Depending on the age of the system, it should be a standard PSU pinout. That being said, I would personally opt for a new mobo too. Driver support and functionality will be much better, but I was trying to answer his specific question...
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