It's not because of it being 64bit, 32 bit programs work fine under a 64 bit OS, the problem is Windows 7. You would still have the same issue if you had the 32 bit version of Win 7 installed.
I found this, you can try it:
To install Matlab 2007 on windows 7
1-Change Windows 7 Theme to the classic one (windows classic)
2-now the Matlab install will work correctly
To use Matlab with other windows 7 themes you have to change java used by matlab.
1- download latest java version and install it.
2- go to C:\Program Files\MATLAB\R2007a\sys\java\jre\win32 you will find a file named jer1.5.0_07 rename it to Original_jer1.5.0_07
3- go to C:\Program Files\Java you will find file named jet6 (jetX for Xversion) copie it to C:\Program Files\MATLAB\R2007a\sys\java\jre\win32
and rename it to jer1.5.0_07
Now you can use matlab with all themes.