i tried to merge 2 objects merged to bones and the merge envelouped weights button was greyed out

That's one of the better features of GATOR (Generalized Attribute Transfer OperatoR) which happens to be disabled in XSI Foundation, but you can however do this in XSI 6 Mod Tool which is free.

.... uh.... (twitch), why would they disable such a usefule and great thing? Ok thanks, ill just have to open it in xsi6 and do what i need to do and send it back to foundation... oh well.

another thing you might be able to answer: In xsi 7, i cant undo something i did>

Splat wrote:...In xsi 7, i cant undo something i did

Go to:
File>Preferences>General
and check the # of undo levels you have and change it if necessary.

Do you know of anyway of getting a series of bones from xsi 6 to xsi5 with out destroying them?

If you mean the fact that 2d bone chains are converted to nulls then that doesn't matter and won't harm anything, but it will add more work for you later if you plan on making any animations, i'm speaking of for example the unit_template_beta.

A workaround would be to merge your weighted objects in Mod Tool then save a weight preset.
In Foundation remove all envelopes and envelope clusters from your scene which consist of multiple envelopes then merge your objects and set the envelope again except this time it will be only 1 enveloped object, then you can apply the weight preset that you saved earlier in Mod Tool, you'll end up with your 2d bone chains and the correct weighting restored to the envelope.

Notes:
For this process set your merge tolerance to 0 when merging your objects so they keep the same number of vertices to maintain accurate weighting so when you apply your saved weight preset in Foundation it will be identical to the envelope weights merged in Mod Tool.