As for the recording requirements, I think those are only guidelines for playback.
I have the HD-PVR unit and recording content just fine, and I have a fairly new macbook (year old)
here are my system specs (note: I went overkill with the RAM, and just went ahead and maxed it out at 4GB)....anyways:
Intel GMA X3100:
Chipset Model: GMA X3100
Type: Display
Bus: Built-In
VRAM (Total): 144 MB
Vendor: Intel (0x8086)
Device ID: 0x2a02
Revision ID: 0x0003
Displays:
Color LCD:
Display Type: LCD
Resolution: 1280 x 800
Depth: 32-bit Color
Built-In: Yes
Core Image: Hardware Accelerated
Main Display: Yes
Mirror: Off
Online: Yes
Quartz Extreme: Supported
Display Connector:
Status: No display connected
Hardware Overview:
Model Name: MacBook
Model Identifier: MacBook3,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.2 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 4 MB
Memory: 4 GB
Bus Speed: 800 MHz
Boot ROM Version: MB31.008E.B02
SMC Version: 1.24f2
Serial Number: W874363EZ63
Sudden Motion Sensor:
State: Enabled
As for my setup, I have the software running on Windows XP SP 2 in boot camp, and have my setup to just do record in 720p.
I tried parallels, and I initally thought it wasn't working right, but I think but it could've been okay, it might have just been that there are some issues with VLC and interlaced video @ 1080i.
The wonderful issues you might run into is what to do with the slightly non-standard TS file that you get from your recording, VLC does fine, but to get it editable in "affordable"/free software you might have to jump through a few hoops.