when I started recording in 2007, my pc specs in terms of computing power back then were just like this. and I made a couple of songs that has 2-8 tracks and everything seems to work well. so to answer the question, interface na lang at dagdag sa RAM and this one is already good. keep in my mind that pc specs has to meet the requirements of which DAW you are going to use. also, I always suggest to get a good reference speaker. I still use my old Samson Resolv for recording at ayun na lang ang natitira sa first recording setup ko after years of upgrades.
+1 with the above but remember, RAM is relative to your OS and your requirements. 2 gig is just about the minimum nowadays. With XP, pwede na yan but I felt better at 4 gig even though only a max of 3.2 gig is usable with that OS.
With win7 and win8, 4 gig is just about the minimum. You can survive at at 2 gigs but some applications may run slowly (photoshop comes to mind). If using 64-bit versions, 4 gig minimum is a must. 64-bit is useful if you require more than 4 gigs ram access. Other than that, 32-bit is fine for most uses, especially with vsts that haven't been ported to 64-bit.
Btw, ram has no bearing on cpu speed, but performance can be increased if your ram is running at dual channel, triple channel, or even quad channel mode. It's important that all sticks be matched in this case. Isa pa, your hard drive also has a bearing on overall performance. It's one reason why laptops tend to have less track counts unless their drives are 7200 rpm, which affects battery life naman.
So many variables.
And another plus on having good monitoring. No point in mixing if you can't hear it right. The only secret is that you should KNOW your speakers. It doesn't matter if they're plain component speakers or very expensive monitors, what matters is that your mixes translate well to other systems.