Weasel-The only way to turn Valygar in is by killing him and then giving his body to Tolgerias(If you have him in your party,Tolgerias will just storm off).You will then get 11250 experience points and your reputation will decrease by 1.At this point,you will be able to ask for information about Imoen.If you do ask,you will get the Ring of the Ram and 500 gold.He will then give some information(nothing that you wouldn't know about) regarding Imoen and how your rescue attempts are futile,yadda yadda.....before casting a dimension door.
EDIT:There is a way to turn Valygar in for the experience and still enter the Planar Sphere.You need to let him join your party,open the door to the Sphere,then go to the Copper Coronet.Remove him from your party and ask him to wait there.After this,talk to him again and say that you plan to give his body to the Cowled Wizard.He will then go hostile.Kill him,and take his body to Tolgerias.You will then get the experience etc. and still be able to enter the Sphere(I'll see wether Tolgerias appears in the Sphere tomorrow,I'm sleepy

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Sorry for the number of edits
[This message has been edited by Brink (edited 02-11-2001).]
[This message has been edited by Brink (edited 02-11-2001).]
[This message has been edited by Brink (edited 02-11-2001).]
[This message has been edited by Brink (edited 02-11-2001).]
[This message has been edited by Brink (edited 02-11-2001).]