asterisk users - Feb 2005 - Integration Asterisk and Siemens Hicom 150

Hi all,
I have this topology:
telco_company>ISND30/PRI/>siemens_hicom_150>classic_analog_users_with_extensions_100-499
and I want to integration asterisk PBX on linux redhat 8 for cca. 4 users.
so, my first question is, which hardware I need in linux server and which in
hicom 150?
and my second... it is possible to connect asterisk PBX directly to PSTN? in
this case I'll have this topology:
telco_company>ISDNBRI>asterisk_PBX_on_linux_>ethernet>some_sw_phone_on_pc_with_extensions_500-510
so, what hw I need in linux server in this case?
thank you for help, milan