Welcome to the forum! Glad you're enjoying Construct.
1) Multiplayer plug-in. - Add multiplayer functions and easy tools for beginners (add a chat as well {in game}).
This is something we're working on and that will be available before the 1.0 release .
2) Xbox and Mac Plug-in-people could save their work to Mac and Xbox.
This is very unlikely to happen anywhere in the near future, though there are a few interested developers who may help with this if we decide to pursue cross-platform capabilities.
3) Make on the layer box (the start position) some "tables" that can show the developers what coordination is the sprite on and etc..
I don't fully understand this, perhaps a mockup would help?
4) Maybe make a sprite and graphic tool.
There is a full picture editor (albeit not to the level of Photoshop, etc) in Construct, if this is what you meant?
And if I could help the development team i would be happy!
I know Abit of:
VB,C#,DOS,python,PHP,HTML etc.
And at graphics:
photoshop,abit flash.
We're always looking for as much help as possible, though all our code is in C++, so any effort would be best focused there.
6) And I have a idea that you could make a data base of sprites the team and people made for the engine and then people would have more resources.(I�d love to help).
This is a really great idea; we've had several posts in the past containing free resources, and doubtless there's many on the internet. It'd be great if someone collected them and made an easily browseable resource center .