I am having trouble connecting my qwest pk5000 to my airport extreme without losing my main and guest networks

Your Qwest is actually an Actiontec combination modem and wireless router. If your 802.11n AirPort Extreme Base Station (AEBSn) is connected downstream of this device, it would typically need to be reconfigured as a bridge. In that case, this mode does NOT support the Guest networking feature.

In order to retain Guest networking, you would need to reconfigure the Qwest device in bridge mode.

If you don't have it already, I would suggest that you download a copy of the User Guide for this Actiontec gateway device directly from the Actiontec support area. It should provide you with information if it is even possible to reconfigure it into bridge mode.

If it can and once configured as such, your AirPort will now be performing as the main Internet router and the gateway will be performing as just a modem. The AirPort is defaulted to perform as an Internet router. If you have made configuration changes to it, it may be better to perform a "factory default" reset on it to get it back to its "out-of-the-box" configuration. Once you verify that your network clients can gain Internet access, you can use the AirPort Utility to configure it based on your networking goals.

You could, but then you would have a double NAT condition, which in itself is not bad. In this state, clients connected to the Actiontec network would not be able to "see" those connected to the AirPort network and vice versa. However, clients on either network would still have Internet access through the Actiontec.