Well as the issue with the router has been covered extensively and there have been no further postings about it from your end I'll take it that that part of the question has been answered to your satisfaction.
Now for the real problem you are going to have 23 boxes connected to a 2003 SBE server well out of the box the SBE edition of 2003 only supports 5 concurrent connections so depending on what you are planing to do you will most likely need to contact a MS Certified Partner to arrange the proper licenses and with that many additional licenses I would be seriously looking at the Enterprise Server edition rather than the Small Business Edition. For Charity applications there are massive discounts from MS as well so you should be buying bare hardware and all the MS products straight from a MS Partner or buy all of the hardware from the same source as the MS products.
Now provided there are no outside connections all you will need is a hub/switch to feed the workstations from the server and this should have at least one built in LAN connection so that can be connected to the Hub/Switch and then all of the computers added to the Domain.
As far as installing the network it should be a simple matter provided you are loading each and every computer your self and are happy to do this. If not hire a consultant or ask if one is willing to perform the work for a reduced fee or for Gratis being that you are setting up for a Charity. If you buy pre-installed software on computers the networking will not be correct and you will have to perform some surgery to get them to join the Domain. The server should be loaded on site and setup as required or again you will have to start digging into the Windows System to create the Domain. It is easier to do this from the start rather then changing things as you go along.