The following line to install fpc used to work:
make.exe install INSTALL_PREFIX=c:\FPC\trunk\ COPYTREE=echo UPXPROG=echo

But now leads to:
.\fpmake.exe install --localunitdir=../.. --globalunitdir=.. --os=win32 --cpu=i386 -o -Ur -o -Xs -o -O2 -o -n -o
-FuC:/FPC/SVN/trunc/rtl/units/i386-win32 -o
-FuC:/FPC/SVN/trunc/packages/hash/units/i386-win32 -o -FuC:/FPC/SVN/trunc/packages/paszlib/units/i386-win32 -o -FuC:/FPC/SVN/trunc/packages/fcl-process/units/i386-win32 -o -FuC:/FPC/SVN/trunc/packages/fpmkunit/units/i386-win32 -o -FE. -o -FUunits/i386-win32 -o -di386 -o -dRELEASE
--compiler=C:/FPC/SVN/trunc/compiler/ppc386.exe --prefix=c:\FPC\trunk\ --unitinstalldir=c:\FPC\trunk\/units/i386-win32/fcl-base -ie The installer encountered the following error:
Failed to create directory "c:\FPC\trunk \bin\"

It appears that 2 issu8es play together.
1) the windows path delim is not translated
2) the \ followed by a space is interpreted as escaped space, and included in the path

I will try without the trailing \ But imho that shouldn't fail, it's a perfectly legal path (afaik)

Try
make.exe install  INSTALL_PREFIX=c:\\FPC\\trunk  COPYTREE=echo UPXPROG=echo

It's a perfectly legal and valid path, but you've forgotten that make is a tool made mostly by C-programmers ;)

It's nothing to do with C or whatever language. It's to do with unix vs win. But it does not even appear to be a make issue, it's fpmake that has an issue

And INSTALL_PREFIX=c:\FPC\trunk (no trailing \) seems to work just fine

I had this problem too -- using fcl-web -- so, I created a hack to compile the FPC 2.5.1 (branches_2_6):

if %myVERSION% equ 2.5.1 (
cd %myFPC%\packages\fastcgi\
del /s fpmake.exe *.ppu *.o

cd %myFPC%\packages\fcl-web\
del /s fpmake.exe *.ppu *.o
)

...before 'make install'.

Marcos Douglas