The ArcGIS 10 License Manager will support your ArcGIS 9.x Desktop clients and any new ArcGIS 10 Desktop clients you deploy.
First you will need to work with ESRI Customer service or your regional vendor to arrange access to the ESRI licensing portal--or issuance of your new Authorization numbers. Your old ArcGIS 9.x License Files will not work to activate the new LM.
The best way to obtain the FlexNet Publisher License Manager and ESRI's authorization tools are to download the ArcGIS Desktop 10.0 DVD installation media .ISO image ( ArcGIS_Desktop10_122519.iso -- 3.94Gb). Then either burn the ISO image to DVD or mount the ISO image and copy out the license manager folders you need for the install.
Use the appropriate installers that are there.
You should immediately install the Service Pack 1 License Manager Patch
gis10sp1-LM-Patch.mspand then the Service Pack 2 License Manager
Installing for the the appropriate OS:Post back if you have any specific questions.