I'm tried, but I can't :\ this is possible?

Not normally, but I suppose an editor can do it.

But... I strongly advice against it. The game is balanced for a new party.

I've alredy finished the four game, but a lose my save :\ and to play the five game I need to finish again the four - not because the experience, and then because the abbilities. I just wanna take my old equippments from third to finish the four again more fast

Story-wise, transferring characters doesn't quite fit either. The two game worlds are on completely different planets.

One cheesy tactic you can use at the beginning of World of Xeen is to straight away go to the Darkside and complete a few quests that have huge experience rewards without requiring combat.

Or just use an editor in this case.

You can simply start a new MM4 game, leave Vertigo and get through the pyramid to the other side to start MM5 in Castleview. You can create fresh level 5 characters in the inn there and play MM5 like a standalone game. It's better balanced this way since XP and other benefits from MM4 make the game too easy. When you've finished MM5 your party will be strong enough to do the MM4 stuff quickly and continue with the WoX extra quests.

Late reply, but:

Transferring saves would not work because items work differently. Many items you get in MM3 can't exist in Xeen, and Xeen segregates items by category. For example, a character whose full inventory contained only armor would not be able to be losslessly transferred.

If you just want to finish 4 quickly, you can do the following:
* Start by going to the darkside, and play there for a while; this will get you tons of XP (because MM5 was designed for higher level parties). If you want to maximize the XP you gain, don't level past 14 until you think you got enough (at level 14 and lower, enemies give double XP).
* Go back to Clouds, and find a mirror. Type "I LOST IT" into the mirror to get that one special weapon you get in MM4 (which is handy because it ignores resistance), and then type Lord Xeen to warp to the MM4 final boss.