Roofus and AngerWound of 360GameSaves.com released an application to access the Xbox (1) and Xbox 360 HDD (all 3 partitions), Memcard or dumps of these, with full write support!
Too many features to list but here are a few:
* FULL Read/Write to Xbox HDDs.
* FULL Read/Write to Xbox 360 HDDs.
* FULL Read/Write to Xbox 360 Memory Units.
* Physical and Logical drive access.
* Support for opening of dumps of both devices.
* Backup/Restore dump options.
You can connect your Xbox 360 HD on your PC via an SATA controller, the memorycard can be connected via USB (see how here or here).