I bought an older Lenovo PC (2005) J series- they were basically giving them away- we had an overstock. If I'm going to be pretty much surfing and downloading-that's about it- will I have problems with slowness compared to a dual core processor, or will the speed be sufficient? It runs on Vista- which for this machine is not ideal.
The processor is plenty for Vista. If it is 32bit Vista, max the memory to 4gb- you'll get the best gains from that. For simply surfing the net and general bullshit, that machine will be fine. If you wish to do some gaming, well, things just got expensive.
BTW, Vista will run circles around XP if you allow SuperFetch to do its thing. It is also far more stable. I currently have machines running XP, XP64, Vista 32 and 64, a few different Linux distributions, and even OSX, and my Vista 64 is the best, followed closely by Vista 32 and XP64. The Linux machines run fine, I just despise the interface, and I can't stand any Apple product I've ever had, and this MacBook is no exception.