Simple answer to the above question is
no.
While wormholes could conceivably exist, a device such as the Stargate as seen on TV will likely never exist for the following reasons :
1. Wormholes are more than likely transient phenomena on a quantum scale
2. Even if wormholes were stable, you would need a singularity at each end to create one
3. The tidal forces inside a wormhole would more than likely rip anything apart that enters them
4. Given one end of a wormhole, there is no physical way to control, or even determine, where the other end is
All these make it a totally impractical way to connect two points in our universe. Furthermore, a device used to create a wormhole would likely be on the same scale in terms of size as the solar system.
Remember, even if aliens did indeed visit earth in acient times ( for which there is no real evidence, despite what some people may want you to believe ), they are still subject to the same physical laws as ourselves. Stargates ? Just not happening, sorry.
