Simple Traffic priorisation

[FreeYourMind]

Hey there,

i would like to establish a (hopefully) rather simple traffic shaping configuration but don`t really know how to start.
Let me describe what i have in mind:

We have a 6Mbit/400kbit ADSL RAM connection.
Unfortunately the dsl modem is only synching with ~4Mbit due to a high signal loss.
There are clients connected to the following interfaces:

LAN (Isolated private Office network)
VLAN100 (Isolated private WLAN network)
VLAN200 (Isolated WLAN network for guests)

The LAN interface builds an untagged VLAN with a few ports assigned on the ProCurve switch, to build an isolated network with pretty much only one office pc and a printer in it.
VLAN100 is tagged on the ProCurve and on the WiFi AP for a private WLAN SSID.
VLAN200 is another SSID that builds our wlan access for guests where certain restrictions take place
(allowing only DNS,HTTP,HTTPS,POP3,SMTP,IMAP)
There is a squid proxy server listening only on the VLAN200 interface for caching purposes and a little bit of content filtering through dansguardian.
Usually there are 30-40 guests on the VLAN200 interface.
What i would like to achieve now is a configuration, where the traffic that comes from the office machine, connected to the LAN interface will always be handled with a higher prority compared to the traffic the guests on VLAN200 generate. Of course with just 4Mbit and a FiFo policy it can happen that the guests eat up every bit of bandwith and there is nothing left for the office machine which can be very frustrating.

I dont really klnow how to do this the right way. Of course i already tried to get informations on my own but it seems the configuration examples i found online doesnt suit the scenario i have in mind, therefor i am looking for help here.

Tahnk you