What's wrong with my planes?FS2004

Hi
I downloaded some planes from simviation.com and I am having a few problems.
One is when using an Embraer 170, the undercarriage moves up and down, the
wheels go underground then back up onto the runway, is this a specific
problem with that plane, not FS2004?
My other main problem is with a lot of the planes I have downloaded, when I
land the aircraft the wheels touch the runway then a few seconds later part
of the plane ends up underground and overall it just kinda skids, tilts then
it stops and says it crashed. Is this a problem with downloading freeware
planes?

Thanks

Daniel

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xbox live GT: poobaboon

Actually Dan, this sounds more like a problem with the particular airfield
scenery that you are using. Does this happen at every airport, or just the
one? Freeware planes are usually just as good as payware and very often
better.