ITEMS with variable [user parameters/system variables]

[zbigiwp]

Helo!
I'd like to create ITEM with user paramaters.
For example:
Free_disk_space_custom
vfs.fs.size[$host_drive_letter,free]

$host_driver_letter is a user parameter created in configuration file.
Is this possible?

Another way that I simulated unsuccesfull is ITEM with enviromental variables:
vfs.file.time["%TMP%\a.txt",modify]
2088:20100822:084950.390 Requested [vfs.file.time["%TMP%\a.txt",modify]]
2088:20100822:084950.390 Sending back [ZBX_NOTSUPPORTED]

Why agent does'nt see system enviroment variables?

I tried using macros but Zabbix does not calcuted in it any values from another ITEMS
for expample
Macro:
{$MYDRIVELETTER} = last(host_drive_letter)
[host_drive_letter - is a ITEM which return user parameter]
does not return any calculated value.