Right off, we would need more information about how many users, different departments, bandwidth / through-put requirements, etc…
Outside of that, Here is a basic layout of one possible configuration:
(Assuming you meant ASA firewall in your question)
[ISP] — <aSA] —  — [3500’s] — [2950s]
The ISP traffic would come in and be filtered by the ASA, which then forwards it to your Core (Running IP routing). The Core would forward traffic to the 3500s, which further deistributes traffic to the 2950 and on to your users / devices
Please provide more details about your requirements so we can better assist you in designing your set-up..