Shefki Kuqi's fine goal put Town ahead, but Lee Bullock's equaliser left the home side's hopes resting on other results.
A draw proved enough in the end though, and Town and the Hammers face an intriguing encounter bearing in mind both teams won 2-1 on the other's ground in the regular season.
Cardiff started brightly against a nervous home side, with Kelvin Davis having to dive to save a deflected Robert Earnshaw shot.
Alan Lee headed a Daniel Gabbidon cross over, and then Lee steered a header narrowly wide from a Gary Croft cross.
With their first real threat, Ipswich went ahead, the recalled Kuqi firing a low 25-yard drive into the corner.
That perked the hosts up and two minutes later Martyn Margetson had to dive to turn away a Darren Bent drive, while Ian Westlake's follow-up was blocked.
Davis made a great save to deny Bullock, but on 40 minutes Cardiff deservedly levelled, Bullock's header deflecting off Jermaine Wright beyond Davis.
Margetson made a great diving save to keep out a curling Jim Magilton free-kick, as the hosts looked to take control.
Tommy Miller sent a left-foot shot narrowly wide from a Matt Richards pass before Lee clipped the outside of the post after a quickly-taken free-kick.
Earnshaw and Bent both saw efforts saved, before Richard Langley's 25-yard drive was caught by Davis in the final moment of danger for the hosts.
Soon after the final whistle, a top-six place was confirmed, and now Ipswich will look to repeat their play-off victory of four years ago.