For build in modules, you have to verify if you have a low-voltage trigger model (such as the Aeon-Lab DSC27103-ZWUS), or a high voltage version like the Philio PAN04 dual-relay. If you specify more exact info on brand/model of the ones you got it is easier to locate datasheet.
Wiring up the high-voltage version is easy, you use the same 3-way (or more) method of house wiring, but instead of having the switching wire provide power to the lightbulb(s), you feed it into the Z-Wave module input contact (S1 or S2 on PAN04). The Z-Wave module will then in turn power the lightbulb(s) via the relay output.
For low-voltage models you have to replace the 3-way wiring, and in most housewiring code structures keep that seperate from high voltage. You can also rely on small battery operated Z-Wave switches, such as the cute Philio PSR04 range (available soon). These then indirectly control the same switch via scenes. I am currently using cheap HAL07 controllers myself, and waiting for the PSR04's to become available.
PS: For switches with build in Z-Wave, there are usually cheap 3-way companion/auxiliary switches available. Those feed direct into the main Z-Wave switch/dimmer (single wire or wireless), example kit --
http://www.amazon.com/GE-Wireless-Lighting-Control-Three-Way/dp/B0035YUOWCPPS: Just noticed the link in your first post, they actually sell rebranded Philio modules there, such as
http://www.intellihome.be/nl/z-wave-tkb-tz04-inbouwschakelaar-2x1-5kw-met-energiemeter.html -- compare that to:
http://philio-tech.com/p_switch.htmYou can also see the high voltage connection diagrams there (unfortunately it does not show the 3-way method, but check to make sure those TZ04 modules are in fact PAN04 rebranded ones first, otherwise you would wire it up like:
http://www.act-remote.com/PCC/images/fig02.gif with the black wire going to the bulb being the one actually going to the Z-Wave module input).