Old PC into a Router problem

ok then im going to take the plunge and turn an old dell into a router so that i can improve the stability of my Internet connection my current router currently conks out about 4 times a day
(i have been searching for 1/2 an hour for this answer as im sure it has been done before but to no avail)
specs are

p3 800Mhz
256 Mb ram
80GB HDD (will try to setup as Nas Also if this is possible)
it currently has 1 x 10Mbs Nic and 2 x 10/100Mbs Nic.

i was planning on using the 10Mbs Nic for incoming Internet connection then using the other 2 as outgoing to my home network roughly 4-5 pcs

i have been looking at software options such as Clarkconnect and smoothwall but was wondering if you had any other opinions. i experimented with smoothwall and it seemed pretty good but very basic

i have a pretty good knowledge of how routers work so wouldnt mind something a bit more complicated if it did the job better my command line coding is next to minimal tho so nothing that complicated thanks.

again if the software allows i would quite like to set it up as a FTP server and NAS

it will connect to 4 comps running Win Xp Pro via a switch and possibly one runnning win 98 via the second 10/100 NIC

or would it be best for me to turn this comp into a server using a form of linux. would this then allow me to route in the same manner

much appreciated

Yak