I want to travel the usa for 6 months starting in december - i will mostly fund this through loans. ideally i want to get a loan as near the time as poss (so am not paying it off before i go) but will i be able to get a visa before getting the loan?

Hate to tell you this - but it's highly unlikely that you will get a 6 month visa to travel in the US.
But do go ahead and apply for one anyway and maybe you will hear from them by December - if you have connections set up over there and clear proof of funds and travel planned then you may get lucky .
If you have US relatives or dual nationality you can more or less stay however long you want - otherwise the only way is if you overstay past your 3 month limit.
If you do that , after you leave you cannot re-enter the states for a min of 10 years - unless they grant you a visa for your next visit . This is highly unlikely as the USCIS are notoriously slow and obstructive - and overstayers come bottom of the pile .

US citizens automatically get a 6 month stay period to visit the UK - we get a max of 3 months to travel over there - via the Visa waiver scheme .
I have been going to the states every year for the last 10 years to see friends and to travel - mainly in Cali - and I have found that the USCIS staff at the airports are becoming ever more intrusive and unhelpful , especially since 9/11.
It's really a shame because it's such a fab place and I have never had a bad time over there .
Check out the London US embassy website re visas and travel rules and regs.
Good luck !

Thanks Tara! Although you've scared me now! We were told by STA that if we had proff of sufficient funding, proof of ties to the UK and return flights home that we should be ok... best hurry up and try and sort this out!

Sorry Sarah - I didn't mean to scare you!
STA have bags of experience and I'm sure their advice is sound . But yes, do get a 'move- on' as I do know that all visa applications -including standard ones like yours - are taking way longer now as they check everything out that's put on the application. Before - they were less thorough and it was a much quicker process.
I have found the the London Embassy Website very helpful - do check it out .

Thanks! Will try and remember to add to this with how I get on. Fingers Crossed!

Just in case anyone is interested I have gotten a visa - I just had to show quite a detailed itinerary including budgeting (so I researched costs of all accomodation, travel, sights etc) and showed bank statements to prove I had the money :)