Saw your question while doing some research on TVTC's (TV Tuner Card) for recording the 2010 World Cup
My 2 cents:
Your setup is almost exactly like my 1st PC. Only difference is mine has 2GB of RAM but a 64MB ATI Radeon GPU. I'm surprised you're able to watch *anything* on there with your external TVTC. It's definitely time to move to a new setup.
Regarding external & internal TVTC's: like pretty much anything else electronic, your connection type makes the biggest difference (in this case, internal vs. USB). External TVTC's connect through a USB port, where as most internal ones use a PCI-E x1 slot on your motherboard. This means the internal TVTC's are hardwired to your system, which is the preferred choice. This route produces better video quality (a lot of factors work into that, actually, such as your cable providers' channel lineup quality, signal strength, etc.,) vs. a USB e-TVTC.
A no-brainer: the more power your rig has, the better video quality you're going to get. The grainy picture you're experiencing has to do with the fact that your system is underpowered. Some basics for your new system:
- @ least a dual core CPU, I'd go for a quad-core AMD or Intel build
- make sure to get the 64-bit version of your OS of choice, Windows 7 Ultimate 64-bit is mine
- @ least 4GB of RAM, I'd suggest 1066MHz at a minimum/if you're on a budget. RAM is *CRUCIAL*. The more, the better.
- the size/number of your HD's totally depend on how much you're going to record/save, but I'd suggest a single 500GB HD for sure
- a decent GPU, like the Radeon HD 5770, to compliment whatever TVTC you decide to get
- make sure you have a power supply that can handle how you plan to use your PC, @ least 500W
- good airflow/cooling inside your case
- DO YOUR RESEARCH, Google/Bing every aspect, it's better to go into it knowing as much as possible vs. building quickly & frying something
Good luck.