> 3) Is it possible to unload a DLL?
  There is a bug for Windows implementation to be fixed.
  As workaround one may apply ".L"/".U" CINT command to load/unload 
DLLs. By the way since CINT doesn't use ROOT "search engine" I hope 
one can use relative pathes under Windows just now as well.
 See (even with "pure" Cint no ROOT):
=====================
E:\root>cint
cint> .L z:\p32\root\bin\Root_Html.dll
cint> .class THtml
===========================================================================
class THtml //Convert class(es) into HTML file(s)
 size=0x20
 (tagnum=228,voffset=-1,isabstract=0,parent=-1,gcomp=0,=~cd=0)
List of base class--------------------------------------------------------
0x0        public: TObject //Basic ROOT object
List of member variable---------------------------------------------------
   . . . 
   . . . 
   . . . 
cint> .U z:\p32\root\bin\Root_Html.dll
cint> .class THtml
Error: class,struct,union or type THtml not defined  FILE: LINE:0
cint>
cint> .U z:\p32\root\bin\Root_Html.dll
Error: G__unloadfile() File "z:\p32\root\bin\Root_Html.dll" not loaded  FILE: LI
NE:0
cint> .L z:\p32\root\bin\Root_Html.dll
cint> .class THtml
===========================================================================
class THtml //Convert class(es) into HTML file(s)
 size=0x20
 (tagnum=228,voffset=-1,isabstract=0,parent=-1,gcomp=0,=~cd=0)
List of base class--------------------------------------------------------
0x0        public: TObject //Basic ROOT object
List of member variable---------------------------------------------------
Defined in THtml
0x0        private: Char_t* fSourceDir //source path
   . . . 
   . . . 
   . . . 
Dr. Valeri Faine (Valery Fine)
    ------------ -------------   Phone: +41 22 767 4921
CERN                             FAX  : +41 22 767 7155
CH-1211 Geneva, 23               mailto:fine@mail.cern.ch 
Switzerland                      http://nicewww.cern.ch/~fine