How to run soapui-3.5.1 on Windows7 64 bit

I've got soapui-3.5.1 installed on my machine and get a bunch of Java errors when trying to start it up. I've tried using different versions of Java and even different versions of soapui, but nothing seems to work. Also, I need to use 3.5.1 or older, anything newer gives me problems with connecting to WSDLs via https through a proxy (which I need to do).

Here are my JAVA_HOME and PATH env vars:
C:\Program Files (x86)\soapui-3.5.1\bin>echo %JAVA_HOME%
C:\Program Files (x86)\Java\jre6

C:\Program Files (x86)\soapui-3.5.1\bin>echo %PATH%
C:\windows\system32;C:\windows;C:\windows\System32\Wbem;C:\windows\System32\Wind
owsPowerShell\v1.0\;C:\Program Files (x86)\Enterprise Vault\EVClient\;C:\Program
Files (x86)\Microsoft Office\Office14;C:\Program Files (x86)\Perforce;c:\Progra
m Files (x86)\Microsoft SQL Server\100\Tools\Binn\VSShell\Common7\IDE\;c:\Progra
m Files (x86)\Microsoft SQL Server\100\Tools\Binn\;c:\Program Files (x86)\Micros
oft SQL Server\100\DTS\Binn\;c:\Program Files\Microsoft SQL Server\100\Tools\Bin
n\;c:\Program Files\Microsoft SQL Server\100\DTS\Binn\;c:\Program Files (x86)\Ja
va\jre6

And I get this error over and over and over when launching soapui-3.5.1:
One chunk of it, but it spits this error out a ton of times and then exits:
UIDefaults.getUI() failed: no ComponentUI class for: javax.swing.JToolBar$Separa
tor[,0,0,0x0,invalid,alignmentX=0.0,alignmentY=0.0,border=,flags=0,maximumSize=,
minimumSize=,preferredSize=,orientation=HORIZONTAL]
java.lang.Error