Here is the perfect board for you.
Soyo P4I845PE ISA - Socket 478 ATX Motherboard with Audio
USB 2.0 AGP 2X/4X and LAN Support
http://www.pricegrabber.com/search_getprod.php/masterid=1673093/
It has 3 ISA slots - and it uses a P4, so you won't have to
shop on Ebay to find it.
http://www.pricegrabber.com/search_techspecs.php?masterid=1673093&tab_id=1
There is one user review here:
http://www.pricegrabber.com/rating_getprodrev.php/product_id=1673093/id_type=M
Manufacturer's website:
http://soyousa.com/products/proddesc.php?id=194
Careful when buying a processor for this. According to the Intel
pricelist, there is a 2.8GHz/FSB533/512KB cache processor still
being manuafactured (a Northwood), and while you probably can still
find a 3.06GHz Northwood processor like it, they may not last long,
as Prescott will replace them.
If you really want a P3 class system, the P2B family with 440BX
chipset is an answer - find all of these on Ebay.
P2B - 3 ISA, Slot 1 based processor
P2B-D - 2 ISA, Dual Slot 1 processor
P2B-DS
P2B-L - 2 ISA, Slot 1 based processor
P2B-S
P2B-LS
P3B-F - 1 or 2 ISA, depending on exact model, Slot 1 based processor.
CUV4X - 1 ISA, socket 370 processor (Coppermine)
- Other members of CUV4X family are PCI only
If this system is for personal use, this guy buys and restores 440BX
based motherboards. He probably has a few processors for them
as well. All you would need to pick up, is compatible RAM, which
can be found on the Crucial.com website. His email address is at
the bottom of this link:
http://tipperlinne.com/p2bmod
Another tool for finding motherboards, is the MOBOT. AFAIK this
database stopped being updated years ago, so you may not be seeing
all possible solutions. Just select the number of ISA slots
desired, and you'll get a huge list.
http://iceberg.pchomeworld.com/cgi-win/mobotGen/mobot.asp
HTH,
Paul