>the i486/586 for speed, can I get one in a tower chassis,

They bust hem at the sam frequency.

>where do I look for such a critter? Computer Shopper has

Findinmg cheap non Apple branded hardware is impossible.
Motorola sells PCI based 604/603/750 MNOtherborad but they are really expensive.

You should wait a bit and look around the Pop platform from IBM which should
become available rsn. (more info can be found on the openppc project pages :
http://www.openppc.org )

Ludo
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http://www.multimania.com/softkid