Hello Chen,
System Export/Import is nothing but system copy only. Since both are windows, you can perform homogeneous system copy.
So your steps would be like this.
1. Upgrade Oracle to 11.2.0.3 on 4.7 32 bit server (Windows 2003)
2. Prepare system for System copy
3. Install SAP R/3 4.7 with Oracle 11.2 on 64-bit Server (Windows 2008 R2).
4. System copy from Windos 2003 to Windows 2008
5. Run SUM to upgrade it to EHP6.
Give a try. All the best.
Best regards,
Srikanth