Yes, you can.
But notice that the "average" value distorts peaks.
Means, if you have one value "100" in between values from 10-12, ths value surely isn't shown as 100 in the graph (because of the average calculation (related to used time period))...
Big ZABBIX is watching you!
(... and my 48 hosts, 4513 items, 1280 triggers via zabbix v1.6 on CentOS 5.0)