Which FXO card to buy

hello friends,
i am just a begineer in asterisk. i want 2 configure asterisk on CENTOS 5.3, and what i want to get from asterisk is below. so plz suggest me which FXO card to buy and on what will be the harware requirements of computer like can i do it in P4 or dual core.

Please note details regarding PBX

a. There are 2 PSTN lines and some 40 extentions.
b.(i) Whenever there is an incoming call, the call is received at Reception Desk, and the operator at Reception Desk then forwards the call to concerned extention.
b.(ii) Whenever there is an incoming call, the caller hears voice recorded at IVR, he may dial extention no., this way call to reception is bypassed.
b.(iii) Whenever there is an incoming fax, the system detect fax tone and forwards automatically to fax machine.
c. Incoming call received at any extention, he can further forward the call to another extention also.
d. When a call is being transferred, the caller hear 'music on hold’
e. Outgoing calls can be configured as ‘Allowed All’ / ‘Allowed Local only’ / ‘Not Allowed’ based on extention no.
f. Every incoming and outgoing call is logged, and printed reports are available, extentionwise and alongwith call costs.
g. All extentions can communicate each other as intercom.
h. When office is closed, the incoming calls are diverted to security office.
i. There is one kind of special telephone instrument also, on that instrument one can interfere / monitor any talk going on at any extention.