TV tuner card and VCR

I have a new Dell machine:

xps 410 E6300 (dual core)
2gb ddr2 SDRAM 667 mhz
2-250 gb RAID 0 hds
Integrated audio
Nvidia 7300 le video card
2407FPW 24" Monitor
Single TV tuner installed by Dell and since replaced - (ATI Theater 550 Pro, ATI PN 102A5030910, SN 23065101289)
Vista Home Premium 32-bit
Two sets of speakers: one older, dual RCA jacks, subwoofer, stereo and also a new Dell speaker bar for my 24" widescreen monitor.

I am using Windows Media Center and with the Dell 2407FPW 24" monitor. When I use a VCR for signal input, the video is somewhat jerky and the sound garbled and of very low volume on both/either set of speakers. I am connected directly to cable (no settop box). Both cable and the VCR work perfectly when connected to a regular TV. I can almost get both good sound and audio using direct vcr to TV tuner card comp video and audio specifying a settop box, but Windows Media Center won't let me complete the setup (no IR cable installed). Regular TV on the TV tuner card works just fine. I do want to be able to use the VCR (many old tapes in the library). Any help would be greatly and deeply appreciated.