indyjones and peris:
Outpost 1.0 Free is not worth trying. When i tested it i had alot of problems and alot of bugs were never resolved.
Outpost 2.0 Pro is worth trying. Its far superior to Kerio 2 and is alot better than Kerio 4.
My views on Outpost 2.0 were lost with the db but i highly recommend it, ive recently ditched Kerio 2 for it myself and i know two other members on the forum have.
Stepping up to Outpost from Kerio 2 is a big step. Lots to get used to but from Kerio 4 its not such a huge step, expect its far more stable
perris, resources is something i know you ask about so ill tell you that without plugins and logging (logging takes a fair but of ram but you can turn it off) its currently using 1,200K of RAM.
If you have more questions or want more detail let me know. Also the sticky in this section i have posted links to the Outpost Guide and Forum.