dual boot problem with Win 7 and ubuntu?

I just installed Win 7 RC on a partition that I reserved, but already had another partition with Ubuntu Linux on it and now will only load Win 7 and can't get back into ubuntu? Anyone know how to fix this?

Oh I was also keeping another partition for XP but since this issue, I have not tried installing XP.

I'm running xp and win7 build 7127 in dual boot ......not having any problems at all...even update new video beta drivers today....all working fine......my advice is dual boot best of both worlds......
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Evga 790 Ultra SLI (P08) | Q9450 @ 3.70 GHZ. |Zalman CNPS 9700
4Gig Patriot G2000LLKN | X-FI Gamer | XFX 260 GTX Black Edition
1-WD VELOCIRAPTOR 300 Gig | 1-Maxtor 300 Gig | 1-WD 500 Gig
Running Raid
Enermax 850| 2-DVD Burners
OS: XP Pro 32 Bit / Win 7 Build 7127 64 Bit

Win7 overwrote the GRUB bootloader. Search around for tips on replacing GRUB. In the future this install order is best to keep from getting headaches...

1st old Windows
2nd new Windows
3rd Linux

Thanks that's what I was wondering. I figured that might have happened due to Linux not even coming up during boot.