vlan expert needed!

[#1]

Hi
I've been tasked with setting up wireless access points around a community centre that I help out.  These will used by people hiring the room(s) rather than staff of the centre.
I need to keep the cost down and am looking at using tp-link access points (WA901ND http://uk.tp-link.com/products/details/?categoryid=239&model=TL-WA901ND) as they have their own passive poe facilities (longest run is about 20m).  However I need to separate this wifi traffic from the office traffic, i.e. enusre that the office pc's are not seen by wifi users.  Their router (an old, but reliable 3com OfficeConnect model) has a vlan feature whereby I can make a vlan (with it's own IP addresses) and assign a specific lan port to it.  The APs can do multi-SSID and vlan but I don't need anything that complicated as the I believe I'll need a managed switch.
If I use a separate, 'simple' switch, e.g. TL-SG108 http://uk.tp-link.com/products/details/?categoryid=1585&model=TL-SG108, purely for the access points and connect this to the 'isolated' lan port will this achieve the result I'm after?  Am I making the right assumption about this vlan implementation being only 'within' the router, as opposed to network-wide vlan set up, i.e. with managed switches etc..  I don't want any communication between the default lan and the new vlan on the router.
Hope someone can help.
Cheers
Andy
EDIT.  May have an alternative to the above.
I've previously used a DIR-615 with DD-WRT plugged into the 3com to provide public wifi and to separate their public-access PCs from the main network and this has worked well.  Rather than change anything in the 3com router I could swap the new switch mentioned above with a DIR-615 and plug the APs into that.  Sounds a simpler, proven solution.  What do you think?

[#2]

You'll also need a separate DHCP server (the VLAN will need to be on a different subnet to your private network). I believe that DD-WRT can support this.

[#3]

Hi
Thanks for your input.
Yep have got DHCP covered.  If I use the vlan option then I'll need to use the DHCP facility of the APs, otherwise, yes, use the DHCP provided by DD-WRT.  This latter is option is looking increasingly better.  It's a know quantity.
Ta
Andy

[#4]

How big is the area you want to cover?
It might just be easier (any maybe more cost effective?) to get a router that has a guest network functionality built into it.

[#5]

if only if was that simple!  It's too big for that suggestion. 
They've already got wifi in the office and the public wifi in the foyer.  I've done a survey for signal strength and in two rooms especially there's no usable signal.  Too much metalwork in the structure.  The longest run of cable is going to be 20m so a fair distance with at least 6 walls in between.  One room's on a different floor as well.