Thailand forum

Once you pay for your plane tickets to Thailand the largest expense is over with.

Some tourists do split their trips when in South East Asia. You can purchase plane tickets or even train tickets while you are in Thailand. From Bangkok you can even take the train to Malaysia if you want to, even on to Singapore.

Other tourists think 6 weeks is too short a time to visit Thailand. It is up to you really. If this may be the only time in the near future when you will have a chance to visit a foreign country why not take some side trips to check out the nearby countries.

Verify that you can stay in Thailand for 6 weeks. Also see if you need a visa for Malaysia. You will probably need a visa for Vietnam, most of the Communist countries require them.
http://www.mfa.go.th/web/2482.php?id=2490
http://www.travelmasti.com/international/malaysia/malaysia-visa.html

Some tourists try to see several countries in less time than you have allowed for your Thailand holiday.

Up to you.

like sirhalberd says, it really is up to you and would depend on both your travel style and what types of things you want to see. in terms of logistics, laos and cambodia are a bit easier to reach on quick side trips from thailand than malaysia and vietnam. then again, if you are really interested in spending your time on the beach, then little land-locked laos may not be your best choice, although the 4,000 islands area does have that laid-back, beach-like vibe.

anyway, i'd say with six weeks at least one side trip is a good idea, if for no other reason than to make your visa situation easier. most folks (check on the regs for your nationality) qualify for a 30-day visa exemption when they arrive by air in thailand. so, you could hang out in thailand for up to 30 days, cross the border (or fly) to another place, and then when you make your way back to thailand, you'll get either a 15 day visa exemption when you arrive by land or another 30 days by air, which has your time completely covered.

i guess if i were looking to visit a place a bit farther away from thailand like malaysia or vietnam, i'd likely look into an open jaw ticket, arriving in bangkok and flying out of KL or HCMC or something like that. assuming it wasn't too expensive to do it that way, you'd save time and effort by not having to get your cookies all the way back to bangers for the return flight.

if you decide to do the full six weeks in thailand, make sure you sort out a 60-day tourist visa before you arrive. that will save you loads of time and effort during your holiday. many thai consulates are offering these for free or reduced fees these days too. regards.

Last Feb we went for four weeks to Thailand. It was not nearly enough to see it all and do it all! We kept saying: next time we'll do this, if we ever go back we're gonna see that... So next Jan/Feb we go for six weeks, only Thailand. And I still have to make choices.
But it depends on how you travel, we like the slow travel, taking daytrains, don't bother delays, staying somewhere an extra night just to wander around.
My advice: don't try to see as much as possible, try to enjoy as much as possible.